193-525: Thorium is a chemical element ; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide ; it is moderately soft, malleable , and has a high melting point . Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state ; it is quite reactive and can ignite in air when finely divided. All known thorium isotopes are unstable. The most stable isotope, Th , has
386-402: A bulk modulus (a measure of resistance to compression of a material) of 54 GPa , about the same as tin 's (58.2 GPa). Aluminium 's is 75.2 GPa; copper's 137.8 GPa; and mild steel's is 160–169 GPa. Thorium is about as hard as soft steel , so when heated it can be rolled into sheets and pulled into wire. Thorium is nearly half as dense as uranium and plutonium and
579-437: A half-life of 14.05 billion years, or about the age of the universe ; it decays very slowly via alpha decay , starting a decay chain named the thorium series that ends at stable Pb . On Earth, thorium and uranium are the only elements with no stable or nearly-stable isotopes that still occur naturally in large quantities as primordial elements . Thorium is estimated to be over three times as abundant as uranium in
772-738: A pure element . In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the same atomic number, or number of protons . Nuclear scientists, however, define a pure element as one that consists of only one isotope. For example, a copper wire is 99.99% chemically pure if 99.99% of its atoms are copper, with 29 protons each. However it is not isotopically pure since ordinary copper consists of two stable isotopes, 69% Cu and 31% Cu, with different numbers of neutrons. However, pure gold would be both chemically and isotopically pure, since ordinary gold consists only of one isotope, Au. Atoms of chemically pure elements may bond to each other chemically in more than one way, allowing
965-412: A BOS process is manufactured in one-twelfth the time. Today, electric arc furnaces (EAF) are a common method of reprocessing scrap metal to create new steel. They can also be used for converting pig iron to steel, but they use a lot of electrical energy (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity. The steel industry
1158-531: A brittle alloy commonly called pig iron . Alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include: manganese , nickel , chromium , molybdenum , boron , titanium , vanadium , tungsten , cobalt , and niobium . Additional elements, most frequently considered undesirable, are also important in steel: phosphorus , sulphur , silicon , and traces of oxygen , nitrogen , and copper . Plain carbon-iron alloys with
1351-684: A carbon-intermediate steel by the 1st century AD. There is evidence that carbon steel was made in Western Tanzania by the ancestors of the Haya people as early as 2,000 years ago by a complex process of "pre-heating" allowing temperatures inside a furnace to reach 1300 to 1400 °C. Evidence of the earliest production of high carbon steel in South Asia is found in Kodumanal in Tamil Nadu ,
1544-444: A change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of compression on the crystals of martensite and tension on the remaining ferrite, with a fair amount of shear on both constituents. If quenching is done improperly, the internal stresses can cause a part to shatter as it cools. At the very least, they cause internal work hardening and other microscopic imperfections. It
1737-540: A considerable amount of time. (See element naming controversy ). Precursors of such controversies involved the nationalistic namings of elements in the late 19th century. For example, lutetium was named in reference to Paris, France. The Germans were reluctant to relinquish naming rights to the French, often calling it cassiopeium . Similarly, the British discoverer of niobium originally named it columbium , in reference to
1930-477: A different element in nuclear reactions , which change an atom's atomic number. Historically, the term "chemical element" meant a substance that cannot be broken down into constituent substances by chemical reactions, and for most practical purposes this definition still has validity. There was some controversy in the 1920s over whether isotopes deserved to be recognized as separate elements if they could be separated by chemical means. The term "(chemical) element"
2123-428: A ferrite BCC crystal form, but at higher carbon content it takes a body-centred tetragonal (BCT) structure. There is no thermal activation energy for the transformation from austenite to martensite. There is no compositional change so the atoms generally retain their same neighbours. Martensite has a lower density (it expands during the cooling) than does austenite, so that the transformation between them results in
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#17328595316642316-643: A few decay products, to have been differentiated from other elements. Most recently, the synthesis of element 118 (since named oganesson ) was reported in October 2006, and the synthesis of element 117 ( tennessine ) was reported in April 2010. Of these 118 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium , atomic number 43; promethium , number 61; astatine , number 85; francium , number 87; neptunium , number 93; and plutonium , number 94. These 94 elements have been detected in
2509-525: A few elements, such as silver and gold , are found uncombined as relatively pure native element minerals . Nearly all other naturally occurring elements occur in the Earth as compounds or mixtures. Air is mostly a mixture of molecular nitrogen and oxygen , though it does contain compounds including carbon dioxide and water , as well as atomic argon , a noble gas which is chemically inert and therefore does not undergo chemical reactions. The history of
2702-583: A hard oxide forms on the metal surface; this is known as stainless steel . Tungsten slows the formation of cementite , keeping carbon in the iron matrix and allowing martensite to preferentially form at slower quench rates, resulting in high-speed steel . The addition of lead and sulphur decrease grain size, thereby making the steel easier to turn , but also more brittle and prone to corrosion. Such alloys are nevertheless frequently used for components such as nuts, bolts, and washers in applications where toughness and corrosion resistance are not paramount. For
2895-445: A hard but brittle martensitic structure. The steel is then tempered, which is just a specialized type of annealing, to reduce brittleness. In this application the annealing (tempering) process transforms some of the martensite into cementite, or spheroidite and hence it reduces the internal stresses and defects. The result is a more ductile and fracture-resistant steel. When iron is smelted from its ore, it contains more carbon than
3088-434: A higher than 2.1% carbon content are known as cast iron . With modern steelmaking techniques such as powder metal forming, it is possible to make very high-carbon (and other alloy material) steels, but such are not common. Cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties. Certain compositions of cast iron, while retaining
3281-412: A narrow range of concentrations of mixtures of carbon and iron that make steel, several different metallurgical structures, with very different properties can form. Understanding such properties is essential to making quality steel. At room temperature , the most stable form of pure iron is the body-centred cubic (BCC) structure called alpha iron or α-iron. It is a fairly soft metal that can dissolve only
3474-402: A new element. He published his findings in 1829, having isolated an impure sample by reducing K[ThF 5 ] (potassium pentafluorothorate(IV)) with potassium metal. Berzelius reused the name of the previous supposed element discovery and named the source mineral thorite. Berzelius made some initial characterisations of the new metal and its chemical compounds: he correctly determined that
3667-500: A pressure of 1 bar and a given temperature (typically at 298.15K). However, for phosphorus, the reference state is white phosphorus even though it is not the most stable allotrope, and the reference state for carbon is graphite, because the structure of graphite is more stable than that of the other allotropes. In thermochemistry , an element is defined to have an enthalpy of formation of zero in its reference state. Several kinds of descriptive categorizations can be applied broadly to
3860-483: A pressure of one atmosphere, are commonly used in characterizing the various elements. While known for most elements, either or both of these measurements is still undetermined for some of the radioactive elements available in only tiny quantities. Since helium remains a liquid even at absolute zero at atmospheric pressure, it has only a boiling point, and not a melting point, in conventional presentations. The density at selected standard temperature and pressure (STP)
4053-470: A quarter is the Th isotope, since Th is one of the daughters of U. The International Union of Pure and Applied Chemistry (IUPAC) reclassified thorium as a binuclidic element in 2013; it had formerly been considered a mononuclidic element . Thorium has three known nuclear isomers (or metastable states), Th, Th, and Th. Th has the lowest known excitation energy of any isomer, measured to be 7.6 ± 0.5 eV . This
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#17328595316644246-459: A range of several hundred thousand years. Ionium–thorium dating is a related process, which exploits the insolubility of thorium (both Th and Th) and thus its presence in ocean sediments to date these sediments by measuring the ratio of Th to Th. Both of these dating methods assume that the proportion of Th to Th is a constant during the period when the sediment layer was formed, that the sediment did not already contain thorium before contributions from
4439-422: A second inner transition series, in the form of the actinides, was not accepted until similarities with the electron structures of the lanthanides had been established; Bohr suggested that the filling of the 5f orbitals may be delayed to after uranium. It was only with the discovery of the first transuranic elements , which from plutonium onward have dominant +3 and +4 oxidation states like the lanthanides, that it
4632-534: A small concentration of carbon, no more than 0.005% at 0 °C (32 °F) and 0.021 wt% at 723 °C (1,333 °F). The inclusion of carbon in alpha iron is called ferrite . At 910 °C, pure iron transforms into a face-centred cubic (FCC) structure, called gamma iron or γ-iron. The inclusion of carbon in gamma iron is called austenite. The more open FCC structure of austenite can dissolve considerably more carbon, as much as 2.1%, (38 times that of ferrite) carbon at 1,148 °C (2,098 °F), which reflects
4825-456: A small group, (the metalloids ), having intermediate properties and often behaving as semiconductors . A more refined classification is often shown in colored presentations of the periodic table. This system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals. The version of this classification used in
5018-448: A steel's final rolling, it is heat treated for strength; however, this is relatively rare. Steel was known in antiquity and was produced in bloomeries and crucibles . The earliest known production of steel is seen in pieces of ironware excavated from an archaeological site in Anatolia ( Kaman-Kalehöyük ) which are nearly 4,000 years old, dating from 1800 BC. Wootz steel
5211-477: A subsequent step. Other materials are often added to the iron/carbon mixture to produce steel with the desired properties. Nickel and manganese in steel add to its tensile strength and make the austenite form of the iron-carbon solution more stable, chromium increases hardness and melting temperature, and vanadium also increases hardness while making it less prone to metal fatigue . To inhibit corrosion, at least 11% chromium can be added to steel so that
5404-420: A white mineral, which he cautiously assumed to be an earth ( oxide in modern chemical nomenclature) of an unknown element. Berzelius had already discovered two elements, cerium and selenium , but he had made a public mistake once, announcing a new element, gahnium , that turned out to be zinc oxide . Berzelius privately named the putative element "thorium" in 1817 and its supposed oxide "thorina" after Thor ,
5597-474: A whole number. For example, the relative atomic mass of chlorine is 35.453 u, which differs greatly from a whole number as it is an average of about 76% chlorine-35 and 24% chlorine-37. Whenever a relative atomic mass value differs by more than ~1% from a whole number, it is due to this averaging effect, as significant amounts of more than one isotope are naturally present in a sample of that element. Chemists and nuclear scientists have different definitions of
5790-672: Is continuously cast into long slabs, cut and shaped into bars and extrusions and heat treated to produce a final product. Today, approximately 96% of steel is continuously cast, while only 4% is produced as ingots. The ingots are then heated in a soaking pit and hot rolled into slabs, billets , or blooms . Slabs are hot or cold rolled into sheet metal or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel , such as I-beams and rails . In modern steel mills these processes often occur in one assembly line , with ore coming in and finished steel products coming out. Sometimes after
5983-404: Is 10 (for tin , element 50). The mass number of an element, A , is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass number, which is written as a superscript on the left hand side of the chemical symbol (e.g., U). The mass number is always an integer and has units of "nucleons". Thus, magnesium-24 (24
Thorium - Misplaced Pages Continue
6176-606: Is a mixture of C (about 98.9%), C (about 1.1%) and about 1 atom per trillion of C. Most (54 of 94) naturally occurring elements have more than one stable isotope. Except for the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of a given element are chemically nearly indistinguishable. All elements have radioactive isotopes (radioisotopes); most of these radioisotopes do not occur naturally. Radioisotopes typically decay into other elements via alpha decay , beta decay , or inverse beta decay ; some isotopes of
6369-406: Is a dimensionless number equal to the atomic mass divided by the atomic mass constant , which equals 1 Da. In general, the mass number of a given nuclide differs in value slightly from its relative atomic mass, since the mass of each proton and neutron is not exactly 1 Da; since the electrons contribute a lesser share to the atomic mass as neutron number exceeds proton number; and because of
6562-405: Is a non-integer due to a 5f–6d overlap.) Among the actinides up to californium , which can be studied in at least milligram quantities, thorium has the highest melting and boiling points and second-lowest density; only actinium is lighter. Thorium's boiling point of 4788 °C is the fifth-highest among all the elements with known boiling points. The properties of thorium vary widely depending on
6755-417: Is a primordial nuclide, having existed in its current form for over ten billion years; it was formed during the r-process , which probably occurs in supernovae and neutron star mergers . These violent events scattered it across the galaxy. The letter "r" stands for "rapid neutron capture", and occurs in core-collapse supernovae, where heavy seed nuclei such as Fe rapidly capture neutrons, running up against
6948-421: Is a rare example of thorium in the formal +3 oxidation state; a formal +2 oxidation state occurs in a derivative. The chloride derivative [Th(C 5 H 5 ) 3 Cl] is prepared by heating thorium tetrachloride with limiting KC 5 H 5 used (other univalent metal cyclopentadienyls can also be used). The alkyl and aryl derivatives are prepared from the chloride derivative and have been used to study
7141-629: Is also very reusable: it is one of the world's most-recycled materials, with a recycling rate of over 60% globally . The noun steel originates from the Proto-Germanic adjective * * stahliją or * * stakhlijan 'made of steel', which is related to * * stahlaz or * * stahliją 'standing firm'. The carbon content of steel is between 0.02% and 2.14% by weight for plain carbon steel ( iron - carbon alloys ). Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make
7334-416: Is always the main element in steel, but many other elements may be present or added. Stainless steels , which are resistant to corrosion and oxidation , typically need an additional 11% chromium . Iron is the base metal of steel. Depending on the temperature, it can take two crystalline forms (allotropic forms): body-centred cubic and face-centred cubic . The interaction of the allotropes of iron with
7527-432: Is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Because of its high tensile strength and low cost, steel is one of the most commonly manufactured materials in the world. Steel is used in buildings, as concrete reinforcing rods, in bridges, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons. Iron
7720-812: Is an ongoing area of scientific study. The lightest elements are hydrogen and helium , both created by Big Bang nucleosynthesis in the first 20 minutes of the universe in a ratio of around 3:1 by mass (or 12:1 by number of atoms), along with tiny traces of the next two elements, lithium and beryllium . Almost all other elements found in nature were made by various natural methods of nucleosynthesis . On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation . New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay , beta decay , spontaneous fission , cluster decay , and other rarer modes of decay. Of
7913-413: Is attributed to its closed nuclear subshell with 142 neutrons. Thorium has a characteristic terrestrial isotopic composition, with atomic weight 232.0377 ± 0.0004 . It is one of only four radioactive elements (along with bismuth, protactinium and uranium) that occur in large enough quantities on Earth for a standard atomic weight to be determined. Thorium nuclei are susceptible to alpha decay because
Thorium - Misplaced Pages Continue
8106-460: Is based on a Latin or other traditional word, for example adopting "gold" rather than "aurum" as the name for the 79th element (Au). IUPAC prefers the British spellings " aluminium " and "caesium" over the U.S. spellings "aluminum" and "cesium", and the U.S. "sulfur" over British "sulphur". However, elements that are practical to sell in bulk in many countries often still have locally used national names, and countries whose national language does not use
8299-562: Is because thorium is likely to form oxide minerals that do not sink into the core; it is classified as a lithophile under the Goldschmidt classification , meaning that it is generally found combined with oxygen. Common thorium compounds are also poorly soluble in water. Thus, even though the refractory elements have the same relative abundances in the Earth as in the Solar System as a whole, there
8492-403: Is common for quench cracks to form when steel is water quenched, although they may not always be visible. There are many types of heat treating processes available to steel. The most common are annealing , quenching , and tempering . Annealing is the process of heating the steel to a sufficiently high temperature to relieve local internal stresses. It does not create a general softening of
8685-400: Is completely miscible in both solid and liquid states with its lighter congener cerium. All but two elements up to bismuth (element 83) have an isotope that is practically stable for all purposes ("classically stable"), with the exceptions being technetium and promethium (elements 43 and 61). All elements from polonium (element 84) onward are measurably radioactive . Th is one of
8878-403: Is desirable. To become steel, it must be reprocessed to reduce the carbon to the correct amount, at which point other elements can be added. In the past, steel facilities would cast the raw steel product into ingots which would be stored until use in further refinement processes that resulted in the finished product. In modern facilities, the initial product is close to the final composition and
9071-436: Is expected to be fissionable with a bare critical mass of 2839 kg, although with steel reflectors this value could drop to 994 kg. Th is not fissionable, but it is fertile as it can be converted to fissile U by neutron capture and subsequent beta decay. Two radiometric dating methods involve thorium isotopes: uranium–thorium dating , based on the decay of U to Th, and ionium–thorium dating , which measures
9264-405: Is extracted from iron ore by removing the oxygen through its combination with a preferred chemical partner such as carbon which is then lost to the atmosphere as carbon dioxide. This process, known as smelting , was first applied to metals with lower melting points, such as tin , which melts at about 250 °C (482 °F), and copper , which melts at about 1,100 °C (2,010 °F), and
9457-489: Is harder than both. It becomes superconductive below 1.4 K . Thorium's melting point of 1750 °C is above both those of actinium (1227 °C) and protactinium (1568 °C). At the start of period 7 , from francium to thorium, the melting points of the elements increase (as in other periods), because the number of delocalised electrons each atom contributes increases from one in francium to four in thorium, leading to greater attraction between these electrons and
9650-408: Is heat treated to contain both a ferritic and martensitic microstructure to produce a formable, high strength steel. Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austenite at room temperature in normally austenite-free low-alloy ferritic steels. By applying strain, the austenite undergoes a phase transition to martensite without
9843-410: Is higher in wavelength than the blackbody emission expected from incandescence at the same temperature, an effect called candoluminescence . It occurs because ThO 2 : Ce acts as a catalyst for the recombination of free radicals that appear in high concentration in a flame, whose deexcitation releases large amounts of energy. The addition of 1% cerium dioxide, as in gas mantles, heightens
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#173285953166410036-473: Is more accessible thorium than heavy platinum group metals in the crust. Natural thorium is usually almost pure Th, which is the longest-lived and most stable isotope of thorium, having a half-life comparable to the age of the universe. Its radioactive decay is the largest single contributor to the Earth's internal heat ; the other major contributors are the shorter-lived primordial radionuclides, which are U, K, and U in descending order of their contribution. (At
10229-460: Is much more similar to the transition metals zirconium and hafnium than to cerium in its ionization energies and redox potentials, and hence also in its chemistry: this transition-metal-like behaviour is the norm in the first half of the actinide series, from actinium to americium. Despite the anomalous electron configuration for gaseous thorium atoms, metallic thorium shows significant 5f involvement. A hypothetical metallic state of thorium that had
10422-687: Is often considered an indicator of economic progress, because of the critical role played by steel in infrastructural and overall economic development . In 1980, there were more than 500,000 U.S. steelworkers. By 2000, the number of steelworkers had fallen to 224,000. The economic boom in China and India caused a massive increase in the demand for steel. Between 2000 and 2005, world steel demand increased by 6%. Since 2000, several Indian and Chinese steel firms have expanded to meet demand, such as Tata Steel (which bought Corus Group in 2007), Baosteel Group and Shagang Group . As of 2017 , though, ArcelorMittal
10615-436: Is often used in characterizing the elements. Density is often expressed in grams per cubic centimetre (g/cm ). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements. When an element has allotropes with different densities, one representative allotrope
10808-544: Is one of the world's most-recycled materials, with a recycling rate of over 60% globally; in the United States alone, over 82,000,000 metric tons (81,000,000 long tons; 90,000,000 short tons) were recycled in the year 2008, for an overall recycling rate of 83%. As more steel is produced than is scrapped, the amount of recycled raw materials is about 40% of the total of steel produced - in 2016, 1,628,000,000 tonnes (1.602 × 10 long tons; 1.795 × 10 short tons) of crude steel
11001-442: Is so low that when it undergoes isomeric transition , the emitted gamma radiation is in the ultraviolet range. The nuclear transition from Th to Th is being investigated for a nuclear clock . Different isotopes of thorium are chemically identical, but have slightly differing physical properties: for example, the densities of pure Th, Th, Th, and Th are respectively expected to be 11.5, 11.6, 11.6, and 11.7 g/cm. The isotope Th
11194-426: Is the mass number) is an atom with 24 nucleons (12 protons and 12 neutrons). Whereas the mass number simply counts the total number of neutrons and protons and is thus an integer, the atomic mass of a particular isotope (or "nuclide") of the element is the mass of a single atom of that isotope, and is typically expressed in daltons (symbol: Da), or universal atomic mass units (symbol: u). Its relative atomic mass
11387-647: Is the most important commercial source of thorium because it occurs in large deposits worldwide, principally in India, South Africa, Brazil, Australia, and Malaysia . It contains around 2.5% thorium on average, although some deposits may contain up to 20%. Monazite is a chemically unreactive mineral that is found as yellow or brown sand; its low reactivity makes it difficult to extract thorium from it. Allanite (chiefly silicates-hydroxides of various metals) can have 0.1–2% thorium and zircon (chiefly zirconium silicate , ZrSiO 4 ) up to 0.4% thorium. Thorium dioxide occurs as
11580-529: Is the world's largest steel producer . In 2005, the British Geological Survey stated China was the top steel producer with about one-third of the world share; Japan , Russia , and the United States were second, third, and fourth, respectively, according to the survey. The large production capacity of steel results also in a significant amount of carbon dioxide emissions inherent related to
11773-532: Is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon ( amorphous carbon , graphite , and diamond ) have densities of 1.8–2.1, 2.267, and 3.515 g/cm , respectively. The elements studied to date as solid samples have eight kinds of crystal structures : cubic , body-centered cubic , face-centered cubic, hexagonal , monoclinic , orthorhombic , rhombohedral , and tetragonal . For some of
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#173285953166411966-404: Is used in nuclear medicine for cancer therapy . Th (alpha emitter with an 18.68 days half-life) can also be used in cancer treatments such as targeted alpha therapies . Th also very occasionally undergoes spontaneous fission rather than alpha decay, and has left evidence of doing so in its minerals (as trapped xenon gas formed as a fission product), but the partial half-life of this process
12159-417: Is used in two different but closely related meanings: it can mean a chemical substance consisting of a single kind of atoms, or it can mean that kind of atoms as a component of various chemical substances. For example, molecules of water (H 2 O) contain atoms of hydrogen (H) and oxygen (O), so water can be said as a compound consisting of the elements hydrogen (H) and oxygen (O) even though it does not contain
12352-519: Is usually detectable, occurring in secular equilibrium with its parent U, and making up at most 0.04% of natural thorium. Thorium only occurs as a minor constituent of most minerals, and was for this reason previously thought to be rare. In fact, it is the 37th most abundant element in the Earth's crust with an abundance of 12 parts per million. In nature, thorium occurs in the +4 oxidation state, together with uranium(IV), zirconium (IV), hafnium(IV), and cerium(IV), and also with scandium , yttrium , and
12545-437: Is very large at over 10 years and alpha decay predominates. In total, 32 radioisotopes have been characterised, which range in mass number from 207 to 238. After Th, the most stable of them (with respective half-lives) are Th (75,380 years), Th (7,917 years), Th (1.92 years), Th (24.10 days), and Th (18.68 days). All of these isotopes occur in nature as trace radioisotopes due to their presence in
12738-429: Is very strong; fullerenes , which have nearly spherical shapes; and carbon nanotubes , which are tubes with a hexagonal structure (even these may differ from each other in electrical properties). The ability of an element to exist in one of many structural forms is known as 'allotropy'. The reference state of an element is defined by convention, usually as the thermodynamically most stable allotrope and physical state at
12931-585: Is widely used. For example, the French chemical terminology distinguishes élément chimique (kind of atoms) and corps simple (chemical substance consisting of a single kind of atoms); the Russian chemical terminology distinguishes химический элемент and простое вещество . Almost all baryonic matter in the universe is composed of elements (among rare exceptions are neutron stars ). When different elements undergo chemical reactions, atoms are rearranged into new compounds held together by chemical bonds . Only
13124-466: The Th ion has no 5f or 6d electrons. Thorium chemistry is therefore largely that of an electropositive metal forming a single diamagnetic ion with a stable noble-gas configuration, indicating a similarity between thorium and the main group elements of the s-block. Thorium and uranium are the most investigated of the radioactive elements because their radioactivity is low enough not to require special handling in
13317-631: The Golconda area in Andhra Pradesh and Karnataka , regions of India , as well as in Samanalawewa and Dehigaha Alakanda, regions of Sri Lanka . This came to be known as wootz steel , produced in South India by about the sixth century BC and exported globally. The steel technology existed prior to 326 BC in the region as they are mentioned in literature of Sangam Tamil , Arabic, and Latin as
13510-480: The International Union of Pure and Applied Chemistry (IUPAC) had recognized a total of 118 elements. The first 94 occur naturally on Earth , and the remaining 24 are synthetic elements produced in nuclear reactions. Save for unstable radioactive elements (radioelements) which decay quickly, nearly all elements are available industrially in varying amounts. The discovery and synthesis of further new elements
13703-625: The Latin alphabet are likely to use the IUPAC element names. According to IUPAC, element names are not proper nouns; therefore, the full name of an element is not capitalized in English, even if derived from a proper noun , as in californium and einsteinium . Isotope names are also uncapitalized if written out, e.g., carbon-12 or uranium-235 . Chemical element symbols (such as Cf for californium and Es for einsteinium), are always capitalized (see below). In
13896-579: The New World . It was used extensively as such by American publications before the international standardization (in 1950). Before chemistry became a science , alchemists designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of atoms combining to form molecules . With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, to depict molecules. Steel Steel
14089-500: The Norse god of thunder. In 1824, after more deposits of the same mineral in Vest-Agder , Norway, were discovered, he retracted his findings, as the mineral (later named xenotime ) proved to be mostly yttrium orthophosphate . In 1828, Morten Thrane Esmark found a black mineral on Løvøya island, Telemark county, Norway. He was a Norwegian priest and amateur mineralogist who studied
14282-586: The cementation process was described in a treatise published in Prague in 1574 and was in use in Nuremberg from 1601. A similar process for case hardening armour and files was described in a book published in Naples in 1589. The process was introduced to England in about 1614 and used to produce such steel by Sir Basil Brooke at Coalbrookdale during the 1610s. The raw material for this process were bars of iron. During
14475-444: The cyclopentadienyl complexes and cyclooctatetraenyls . Like many of the early and middle actinides (up to americium , and also expected for curium ), thorium forms a cyclooctatetraenide complex: the yellow Th(C 8 H 8 ) 2 , thorocene . It is isotypic with the better-known analogous uranium compound uranocene . It can be prepared by reacting K 2 C 8 H 8 with thorium tetrachloride in tetrahydrofuran (THF) at
14668-419: The hardness , quenching behaviour , need for annealing , tempering behaviour , yield strength , and tensile strength of the resulting steel. The increase in steel's strength compared to pure iron is possible only by reducing iron's ductility. Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in
14861-423: The kinetic isotope effect is significant). Thus, all carbon isotopes have nearly identical chemical properties because they all have six electrons, even though they may have 6 to 8 neutrons. That is why atomic number, rather than mass number or atomic weight , is considered the identifying characteristic of an element. The symbol for atomic number is Z . Isotopes are atoms of the same element (that is, with
15054-432: The neutron drip line , as neutrons are captured much faster than the resulting nuclides can beta decay back toward stability. Neutron capture is the only way for stars to synthesise elements beyond iron because of the increased Coulomb barriers that make interactions between charged particles difficult at high atomic numbers and the fact that fusion beyond Fe is endothermic . Because of the abrupt loss of stability past Bi,
15247-405: The nuclear binding energy and electron binding energy. For example, the atomic mass of chlorine-35 to five significant digits is 34.969 Da and that of chlorine-37 is 36.966 Da. However, the relative atomic mass of each isotope is quite close to its mass number (always within 1%). The only isotope whose atomic mass is exactly a natural number is C, which has a mass of 12 Da; because
15440-445: The 17th century, it was realized that the best steel came from oregrounds iron of a region north of Stockholm , Sweden. This was still the usual raw material source in the 19th century, almost as long as the process was used. Crucible steel is steel that has been melted in a crucible rather than having been forged , with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt
15633-470: The 17th century, the first step in European steel production has been the smelting of iron ore into pig iron in a blast furnace . Originally employing charcoal, modern methods use coke , which has proven more economical. In these processes, pig iron made from raw iron ore was refined (fined) in a finery forge to produce bar iron , which was then used in steel-making. The production of steel by
15826-607: The 17th century, with the introduction of the blast furnace and production of crucible steel . This was followed by the Bessemer process in England in the mid-19th century, and then by the open-hearth furnace . With the invention of the Bessemer process, a new era of mass-produced steel began. Mild steel replaced wrought iron . The German states were the major steel producers in Europe in
16019-475: The 19th century. American steel production was centred in Pittsburgh , Bethlehem, Pennsylvania , and Cleveland until the late 20th century. Currently, world steel production is centered in China, which produced 54% of the world's steel in 2023. Further refinements in the process, such as basic oxygen steelmaking (BOS), largely replaced earlier methods by further lowering the cost of production and increasing
16212-416: The 5f and 6d subshells in the early actinides are very close in energy, even more so than the 4f and 5d subshells of the lanthanides: thorium's 6d subshells are lower in energy than its 5f subshells, because its 5f subshells are not well-shielded by the filled 6s and 6p subshells and are destabilised. This is due to relativistic effects , which become stronger near the bottom of the periodic table, specifically
16405-638: The 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium , element 43 and promethium , element 61, which have no stable isotopes). Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of
16598-499: The American electrical engineer Robert Bowie Owens studied the radiation from thorium; initial observations showed that it varied significantly. It was determined that these variations came from a short-lived gaseous daughter of thorium, which they found to be a new element. This element is now named radon , the only one of the rare radioelements to be discovered in nature as a daughter of thorium rather than uranium. After accounting for
16791-600: The Arabs from Persia, who took it from India. It was originally created from several different materials including various trace elements , apparently ultimately from the writings of Zosimos of Panopolis . In 327 BC, Alexander the Great was rewarded by the defeated King Porus , not with gold or silver but with 30 pounds of steel. A recent study has speculated that carbon nanotubes were included in its structure, which might explain some of its legendary qualities, though, given
16984-547: The Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare-earth elements . Thorium was discovered in 1828 by the Norwegian amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jacob Berzelius , who named it after Thor , the Norse god of thunder and war, because of its power. Its first applications were developed in the late 19th century. Thorium's radioactivity
17177-487: The French, Italians, Greeks, Portuguese and Poles prefer "azote/azot/azoto" (from roots meaning "no life") for "nitrogen". For purposes of international communication and trade, the official names of the chemical elements both ancient and more recently recognized are decided by the International Union of Pure and Applied Chemistry (IUPAC), which has decided on a sort of international English language, drawing on traditional English names even when an element's chemical symbol
17370-463: The Linz-Donawitz process of basic oxygen steelmaking (BOS), developed in 1952, and other oxygen steel making methods. Basic oxygen steelmaking is superior to previous steelmaking methods because the oxygen pumped into the furnace limited impurities, primarily nitrogen, that previously had entered from the air used, and because, with respect to the open hearth process, the same quantity of steel from
17563-502: The [Rn]6d7s configuration with the 5f orbitals above the Fermi level should be hexagonal close packed like the group 4 elements titanium, zirconium, and hafnium, and not face-centred cubic as it actually is. The actual crystal structure can only be explained when the 5f states are invoked, proving that thorium is metallurgically a true actinide. Tetravalent thorium compounds are usually colourless or yellow, like those of silver or lead, as
17756-401: The alloying elements, primarily carbon, gives steel and cast iron their range of unique properties. In pure iron, the crystal structure has relatively little resistance to the iron atoms slipping past one another, and so pure iron is quite ductile , or soft and easily formed. In steel, small amounts of carbon, other elements, and inclusions within the iron act as hardening agents that prevent
17949-615: The ancient ocean. Thorium is a moderately soft, paramagnetic , bright silvery radioactive actinide metal that can be bent or shaped. In the periodic table , it lies to the right of actinium , to the left of protactinium , and below cerium . Pure thorium is very ductile and, as normal for metals, can be cold-rolled , swaged , and drawn . At room temperature, thorium metal has a face-centred cubic crystal structure; it has two other forms, one at high temperature (over 1360 °C; body-centred cubic) and one at high pressure (around 100 GPa; body-centred tetragonal ). Thorium metal has
18142-487: The atomic masses of the elements (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers. The naming of various substances now known as elements precedes the atomic theory of matter, as names were given locally by various cultures to various minerals, metals, compounds, alloys, mixtures, and other materials, though at the time it was not known which chemicals were elements and which compounds. As they were identified as elements,
18335-436: The austenite grain boundaries until the percentage of carbon in the grains has decreased to the eutectoid composition (0.8% carbon), at which point the pearlite structure forms. For steels that have less than 0.8% carbon (hypoeutectoid), ferrite will first form within the grains until the remaining composition rises to 0.8% of carbon, at which point the pearlite structure will form. No large inclusions of cementite will form at
18528-471: The austenite is for it to precipitate out of solution as cementite , leaving behind a surrounding phase of BCC iron called ferrite with a small percentage of carbon in solution. The two, cementite and ferrite, precipitate simultaneously producing a layered structure called pearlite , named for its resemblance to mother of pearl . In a hypereutectoid composition (greater than 0.8% carbon), the carbon will first precipitate out as large inclusions of cementite at
18721-494: The boundaries in hypoeutectoid steel. The above assumes that the cooling process is very slow, allowing enough time for the carbon to migrate. As the rate of cooling is increased the carbon will have less time to migrate to form carbide at the grain boundaries but will have increasingly large amounts of pearlite of a finer and finer structure within the grains; hence the carbide is more widely dispersed and acts to prevent slip of defects within those grains, resulting in hardening of
18914-413: The chemical substances (di)hydrogen (H 2 ) and (di)oxygen (O 2 ), as H 2 O molecules are different from H 2 and O 2 molecules. For the meaning "chemical substance consisting of a single kind of atoms", the terms "elementary substance" and "simple substance" have been suggested, but they have not gained much acceptance in English chemical literature, whereas in some other languages their equivalent
19107-455: The combination, bronze, which has a melting point lower than 1,083 °C (1,981 °F). In comparison, cast iron melts at about 1,375 °C (2,507 °F). Small quantities of iron were smelted in ancient times, in the solid-state, by heating the ore in a charcoal fire and then welding the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in
19300-429: The contribution of radon, Rutherford, now working with the British physicist Frederick Soddy , showed how thorium decayed at a fixed rate over time into a series of other elements in work dating from 1900 to 1903. This observation led to the identification of the half-life as one of the outcomes of the alpha particle experiments that led to the disintegration theory of radioactivity . The biological effect of radiation
19493-408: The dalton is defined as 1/12 of the mass of a free neutral carbon-12 atom in the ground state. The standard atomic weight (commonly called "atomic weight") of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit. This number may be a fraction that is not close to
19686-439: The decay chains of Th, U, U, and Np : the last of these is long extinct in nature due to its short half-life (2.14 million years), but is continually produced in minute traces from neutron capture in uranium ores. All of the remaining thorium isotopes have half-lives that are less than thirty days and the majority of these have half-lives that are less than ten minutes. Th (half-life 22 minutes) occurs naturally as
19879-461: The decay of plutonium and curium isotopes, and thorium was enriched relative to uranium by the decay of U to Th and the natural depletion of U, but these sources have long since decayed and no longer contribute. In the Earth's crust, thorium is much more abundant: with an abundance of 8.1 g/ tonne , it is one of the most abundant of the heavy elements, almost as abundant as lead (13 g/tonne) and more abundant than tin (2.1 g/tonne). This
20072-409: The decay of uranium, and that the thorium cannot migrate within the sediment layer. A thorium atom has 90 electrons, of which four are valence electrons . Four atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, 7s, and 7p. Despite thorium's position in the f-block of the periodic table, it has an anomalous [Rn]6d7s electron configuration in the ground state, as
20265-465: The degree of impurities in the sample. The major impurity is usually thorium dioxide ThO 2 ); even the purest thorium specimens usually contain about a tenth of a per cent of the dioxide. Experimental measurements of its density give values between 11.5 and 11.66 g/cm: these are slightly lower than the theoretically expected value of 11.7 g/cm calculated from thorium's lattice parameters , perhaps due to microscopic voids forming in
20458-444: The dioxide. In bulk, the reaction of pure thorium with air is slow, although corrosion may occur after several months; most thorium samples are contaminated with varying degrees of the dioxide, which greatly accelerates corrosion. Such samples slowly tarnish, becoming grey and finally black at the surface. At standard temperature and pressure , thorium is slowly attacked by water, but does not readily dissolve in most common acids, with
20651-416: The discovery and use of elements began with early human societies that discovered native minerals like carbon , sulfur , copper and gold (though the modern concept of an element was not yet understood). Attempts to classify materials such as these resulted in the concepts of classical elements , alchemy , and similar theories throughout history. Much of the modern understanding of elements developed from
20844-576: The disposal of nuclear waste, but most of them have not yet been fully characterised, especially regarding their structural properties. For example, thorium nitrate is produced by reacting thorium hydroxide with nitric acid: it is soluble in water and alcohols and is an important intermediate in the purification of thorium and its compounds. Thorium complexes with organic ligands, such as oxalate , citrate , and EDTA , are much more stable. In natural thorium-containing waters, organic thorium complexes usually occur in concentrations orders of magnitude higher than
21037-400: The economies of melting and casting, can be heat treated after casting to make malleable iron or ductile iron objects. Steel is distinguishable from wrought iron (now largely obsolete), which may contain a small amount of carbon but large amounts of slag . Iron is commonly found in the Earth's crust in the form of an ore , usually an iron oxide, such as magnetite or hematite . Iron
21230-552: The effect by increasing emissivity in the visible region of the spectrum; but because cerium, unlike thorium, can occur in multiple oxidation states, its charge and hence visible emissivity will depend on the region on the flame it is found in (as such regions vary in their chemical composition and hence how oxidising or reducing they are). Several binary thorium chalcogenides and oxychalcogenides are also known with sulfur , selenium , and tellurium . All four thorium tetrahalides are known, as are some low-valent bromides and iodides:
21423-406: The elements are available by name, atomic number, density, melting point, boiling point and chemical symbol , as well as ionization energy . The nuclides of stable and radioactive elements are also available as a list of nuclides , sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in the form of
21616-470: The elements are often summarized using the periodic table, which powerfully and elegantly organizes the elements by increasing atomic number into rows ( "periods" ) in which the columns ( "groups" ) share recurring ("periodic") physical and chemical properties. The table contains 118 confirmed elements as of 2021. Although earlier precursors to this presentation exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended
21809-480: The elements can be uniquely sequenced by atomic number, conventionally from lowest to highest (as in a periodic table), sets of elements are sometimes specified by such notation as "through", "beyond", or "from ... through", as in "through iron", "beyond uranium", or "from lanthanum through lutetium". The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities), as in "lighter than carbon" or "heavier than lead", though
22002-428: The elements together. In air, thorium burns to form ThO 2 , which has the fluorite structure. Thorium dioxide is a refractory material , with the highest melting point (3390 °C) of any known oxide. It is somewhat hygroscopic and reacts readily with water and many gases; it dissolves easily in concentrated nitric acid in the presence of fluoride. When heated in air, thorium dioxide emits intense blue light;
22195-413: The elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic number greater than 82. Of the 80 elements with at least one stable isotope, 26 have only one stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes for a single element
22388-474: The elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins. Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between metals , which readily conduct electricity , nonmetals , which do not, and
22581-446: The end of the 1930s. Up to the late 19th century, chemists unanimously agreed that thorium and uranium were the heaviest members of group 4 and group 6 respectively; the existence of the lanthanides in the sixth row was considered to be a one-off fluke. In 1892, British chemist Henry Bassett postulated a second extra-long periodic table row to accommodate known and undiscovered elements, considering thorium and uranium to be analogous to
22774-401: The exception of hydrochloric acid , where it dissolves leaving a black insoluble residue of ThO(OH,Cl)H. It dissolves in concentrated nitric acid containing a small quantity of catalytic fluoride or fluorosilicate ions; if these are not present, passivation by the nitrate can occur, as with uranium and plutonium. Most binary compounds of thorium with nonmetals may be prepared by heating
22967-492: The existing names for anciently known elements (e.g., gold, mercury, iron) were kept in most countries. National differences emerged over the element names either for convenience, linguistic niceties, or nationalism. For example, German speakers use "Wasserstoff" (water substance) for "hydrogen", "Sauerstoff" (acid substance) for "oxygen" and "Stickstoff" (smothering substance) for "nitrogen"; English and some other languages use "sodium" for "natrium", and "potassium" for "kalium"; and
23160-630: The explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System . At over 1.9 × 10 years, over a billion times longer than the estimated age of the universe, bismuth-209 has the longest known alpha decay half-life of any isotope, and is almost always considered on par with the 80 stable elements. The heaviest elements (those beyond plutonium, element 94) undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized . There are now 118 known elements. In this context, "known" means observed well enough, even from just
23353-625: The finest steel in the world exported to the Roman, Egyptian, Chinese and Arab worlds at that time – what they called Seric Iron . A 200 BC Tamil trade guild in Tissamaharama , in the South East of Sri Lanka, brought with them some of the oldest iron and steel artifacts and production processes to the island from the classical period . The Chinese and locals in Anuradhapura , Sri Lanka had also adopted
23546-573: The fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily. All of these temperatures could be reached with ancient methods used since the Bronze Age . Since the oxidation rate of iron increases rapidly beyond 800 °C (1,470 °F), it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iron oxides, results in an alloy ( pig iron ) that retains too much carbon to be called steel. The excess carbon and other impurities are removed in
23739-503: The form of charcoal) in a crucible, was produced in Merv by the 9th to 10th century AD. In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, inhomogeneous steel, and a precursor to the modern Bessemer process that used partial decarburization via repeated forging under a cold blast . Since
23932-529: The formation of Earth, they are certain to have completely decayed, and if present in novae, are in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element synthesized, in 1937, though trace amounts of technetium have since been found in nature (and also the element may have been discovered naturally in 1925). This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally occurring rare elements. List of
24125-464: The gelatinous hydroxide Th(OH) 4 forms and precipitates out (though equilibrium may take weeks to be reached, because the polymerisation usually slows down before the precipitation). As a hard Lewis acid , Th favours hard ligands with oxygen atoms as donors: complexes with sulfur atoms as donors are less stable and are more prone to hydrolysis. High coordination numbers are the rule for thorium due to its large size. Thorium nitrate pentahydrate
24318-462: The great insolubility of thorium dioxide, thorium does not usually spread quickly through the environment when released. The Th ion is soluble, especially in acidic soils, and in such conditions the thorium concentration can be higher. In 1815, the Swedish chemist Jöns Jacob Berzelius analysed an unusual sample of gadolinite from a copper mine in Falun , central Sweden. He noted impregnated traces of
24511-431: The half-lives predicted for the observationally stable lead isotopes range from 10 to 10 years. Elements with atomic numbers 43, 61, and 83 through 94 are unstable enough that their radioactive decay can be detected. Three of these elements, bismuth (element 83), thorium (90), and uranium (92) have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced
24704-599: The hardenability of thick sections. High strength low alloy steel has small additions (usually < 2% by weight) of other elements, typically 1.5% manganese, to provide additional strength for a modest price increase. Recent corporate average fuel economy (CAFE) regulations have given rise to a new variety of steel known as Advanced High Strength Steel (AHSS). This material is both strong and ductile so that vehicle structures can maintain their current safety levels while using less material. There are several commercially available grades of AHSS, such as dual-phase steel , which
24897-399: The heaviest elements also undergo spontaneous fission . Isotopes that are not radioactive, are termed "stable" isotopes. All known stable isotopes occur naturally (see primordial nuclide ). The many radioisotopes that are not found in nature have been characterized after being artificially produced. Certain elements have no stable isotopes and are composed only of radioisotopes: specifically
25090-488: The heavy elements before the formation of the Solar System. For example, at over 1.9 × 10 years, over a billion times longer than the estimated age of the universe, bismuth-209 has the longest known alpha decay half-life of any isotope. The last 24 elements (those beyond plutonium, element 94) undergo radioactive decay with short half-lives and cannot be produced as daughters of longer-lived elements, and thus are not known to occur in nature at all. 1 The properties of
25283-446: The inorganic complexes, even when the concentrations of inorganic ligands are much greater than those of organic ligands. In January 2021, the aromaticity has been observed in a large metal cluster anion consisting of 12 bismuth atoms stabilised by a center thorium cation. This compound was shown to be surprisingly stable, unlike many previous known aromatic metal clusters . Most of the work on organothorium compounds has focused on
25476-404: The laboratory. Thorium is a highly reactive and electropositive metal. With a standard reduction potential of −1.90 V for the Th /Th couple, it is somewhat more electropositive than zirconium or aluminium. Finely divided thorium metal can exhibit pyrophoricity , spontaneously igniting in air. When heated in air, thorium turnings ignite and burn with a brilliant white light to produce
25669-401: The lanthanides, instead of being the heavier congener of hafnium in a fourth d-block row. Chemical element A chemical element is a chemical substance whose atoms all have the same number of protons . The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus. Atoms of
25862-418: The lanthanides. In 1913, Danish physicist Niels Bohr published a theoretical model of the atom and its electron orbitals, which soon gathered wide acceptance. The model indicated that the seventh row of the periodic table should also have f-shells filling before the d-shells that were filled in the transition elements, like the sixth row with the lanthanides preceding the 5d transition metals. The existence of
26055-541: The later recognition that the rare earths were mostly trivalent and thorium was tetravalent, Mendeleev moved cerium and thorium to group IV in 1871, which also contained the modern carbon group (group 14) and titanium group (group 4), because their maximum oxidation state was +4. Cerium was soon removed from the main body of the table and placed in a separate lanthanide series; thorium was left with group 4 as it had similar properties to its supposed lighter congeners in that group, such as titanium and zirconium. While thorium
26248-461: The light becomes white when ThO 2 is mixed with its lighter homologue cerium dioxide ( CeO 2 , ceria): this is the basis for its previously common application in gas mantles . A flame is not necessary for this effect: in 1901, it was discovered that a hot Welsbach gas mantle (using ThO 2 with 1% CeO 2 ) remained at "full glow" when exposed to a cold unignited mixture of flammable gas and air. The light emitted by thorium dioxide
26441-622: The light source in gas mantles , but these uses have become marginal. It has been suggested as a replacement for uranium as nuclear fuel in nuclear reactors , and several thorium reactors have been built. Thorium is also used in strengthening magnesium , coating tungsten wire in electrical equipment, controlling the grain size of tungsten in electric lamps , high-temperature crucibles, and glasses including camera and scientific instrument lenses. Other uses for thorium include heat-resistant ceramics, aircraft engines , and in light bulbs . Ocean science has utilised Pa /Th isotope ratios to understand
26634-411: The longer-lived Pa, and this process is often used to check the results of uranium–thorium dating. Uranium–thorium dating is commonly used to determine the age of calcium carbonate materials such as speleothem or coral , because uranium is more soluble in water than thorium and protactinium, which are selectively precipitated into ocean-floor sediments , where their ratios are measured. The scheme has
26827-439: The main production route. At the end of 2008, the steel industry faced a sharp downturn that led to many cut-backs. In 2021, it was estimated that around 7% of the global greenhouse gas emissions resulted from the steel industry. Reduction of these emissions are expected to come from a shift in the main production route using cokes, more recycling of steel and the application of carbon capture and storage technology. Steel
27020-450: The metal ions as their charge increases from one to four. After thorium, there is a new downward trend in melting points from thorium to plutonium , where the number of f electrons increases from about 0.4 to about 6: this trend is due to the increasing hybridisation of the 5f and 6d orbitals and the formation of directional bonds resulting in more complex crystal structures and weakened metallic bonding. (The f-electron count for thorium metal
27213-513: The metal when it is cast. These values lie between those of its neighbours actinium (10.1 g/cm) and protactinium (15.4 g/cm), part of a trend across the early actinides. Thorium can form alloys with many other metals. Addition of small proportions of thorium improves the mechanical strength of magnesium , and thorium-aluminium alloys have been considered as a way to store thorium in proposed future thorium nuclear reactors. Thorium forms eutectic mixtures with chromium and uranium, and it
27406-605: The minerals in Telemark, where he served as vicar . He commonly sent the most interesting specimens, such as this one, to his father, Jens Esmark , a noted mineralogist and professor of mineralogy and geology at the Royal Frederick University in Christiania (today called Oslo ). The elder Esmark determined that it was not a known mineral and sent a sample to Berzelius for examination. Berzelius determined that it contained
27599-450: The most part, however, p-block elements such as sulphur, nitrogen , phosphorus , and lead are considered contaminants that make steel more brittle and are therefore removed from steel during the melting processing. The density of steel varies based on the alloying constituents but usually ranges between 7,750 and 8,050 kg/m (484 and 503 lb/cu ft), or 7.75 and 8.05 g/cm (4.48 and 4.65 oz/cu in). Even in
27792-446: The movement of dislocations . The carbon in typical steel alloys may contribute up to 2.14% of its weight. Varying the amount of carbon and many other alloying elements, as well as controlling their chemical and physical makeup in the final steel (either as solute elements, or as precipitated phases), impedes the movement of the dislocations that make pure iron ductile, and thus controls and enhances its qualities. These qualities include
27985-465: The nature of the Th–C sigma bond . Other organothorium compounds are not well-studied. Tetrabenzylthorium, Th(CH 2 C 6 H 5 ) 4 , and tetraallylthorium, Th(CH 2 CH=CH 2 ) 4 , are known, but their structures have not been determined. They decompose slowly at room temperature. Thorium forms the monocapped trigonal prismatic anion [Th(CH 3 ) 7 ] , heptamethylthorate(IV), which forms
28178-604: The oxidation of ammonia to nitric acid. Thorium was first observed to be radioactive in 1898, by the German chemist Gerhard Carl Schmidt and later that year, independently, by the Polish-French physicist Marie Curie . It was the second element that was found to be radioactive, after the 1896 discovery of radioactivity in uranium by French physicist Henri Becquerel . Starting from 1899, the New Zealand physicist Ernest Rutherford and
28371-418: The periodic table, which groups together elements with similar chemical properties (and usually also similar electronic structures). The atomic number of an element is equal to the number of protons in each atom, and defines the element. For example, all carbon atoms contain 6 protons in their atomic nucleus ; so the atomic number of carbon is 6. Carbon atoms may have different numbers of neutrons; atoms of
28564-426: The periodic tables presented here includes: actinides , alkali metals , alkaline earth metals , halogens , lanthanides , transition metals , post-transition metals , metalloids , reactive nonmetals , and noble gases . In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense. Similarly,
28757-449: The product but only locally relieves strains and stresses locked up within the material. Annealing goes through three phases: recovery , recrystallization , and grain growth . The temperature required to anneal a particular steel depends on the type of annealing to be achieved and the alloying constituents. Quenching involves heating the steel to create the austenite phase then quenching it in water or oil . This rapid cooling results in
28950-693: The production methods of creating wootz steel from the Chera Dynasty Tamils of South India by the 5th century AD. In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds, capable of producing high-carbon steel. Since the technology was acquired from the Tamilians from South India, the origin of steel technology in India can be conservatively estimated at 400–500 BC. The manufacture of wootz steel and Damascus steel , famous for its durability and ability to hold an edge, may have been taken by
29143-412: The pure element to exist in multiple chemical structures ( spatial arrangements of atoms ), known as allotropes , which differ in their properties. For example, carbon can be found as diamond , which has a tetrahedral structure around each carbon atom; graphite , which has layers of carbon atoms with a hexagonal structure stacked on top of each other; graphene , which is a single layer of graphite that
29336-426: The quality of the final product. Today more than 1.6 billion tons of steel is produced annually. Modern steel is generally identified by various grades defined by assorted standards organizations . The modern steel industry is one of the largest manufacturing industries in the world, but also one of the most energy and greenhouse gas emission intense industries, contributing 8% of global emissions. However, steel
29529-427: The r-process (the other being uranium), and also because it has slowly been decaying away from the moment it formed. The only primordial elements rarer than thorium are thulium , lutetium , tantalum, and rhenium, the odd-numbered elements just before the third peak of r-process abundances around the heavy platinum group metals, as well as uranium. In the distant past the abundances of thorium and uranium were enriched by
29722-405: The r-process is the only process of stellar nucleosynthesis that can create thorium and uranium; all other processes are too slow and the intermediate nuclei alpha decay before they capture enough neutrons to reach these elements. In the universe, thorium is among the rarest of the primordial elements at rank 77th in cosmic abundance because it is one of the two elements that can be produced only in
29915-600: The rare mineral thorianite . Due to its being isotypic with uranium dioxide , these two common actinide dioxides can form solid-state solutions and the name of the mineral changes according to the ThO 2 content. Thorite (chiefly thorium silicate , ThSiO 4 ), also has a high thorium content and is the mineral in which thorium was first discovered. In thorium silicate minerals, the Th and SiO 4− 4 ions are often replaced with M (where M = Sc, Y, or Ln) and phosphate ( PO 3− 4 ) ions respectively. Because of
30108-455: The ratio of Th to Th. These rely on the fact that Th is a primordial radioisotope, but Th only occurs as an intermediate decay product in the decay chain of U. Uranium–thorium dating is a relatively short-range process because of the short half-lives of U and Th relative to the age of the Earth: it is also accompanied by a sister process involving the alpha decay of U into Th, which very quickly becomes
30301-772: The reactive nonmetals and the noble gases are nonmetals viewed in the broader sense. In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals. Another commonly used basic distinction among the elements is their state of matter (phase), whether solid , liquid , or gas , at standard temperature and pressure (STP). Most elements are solids at STP, while several are gases. Only bromine and mercury are liquid at 0 degrees Celsius (32 degrees Fahrenheit) and 1 atmosphere pressure; caesium and gallium are solid at that temperature, but melt at 28.4°C (83.2°F) and 29.8°C (85.6°F), respectively. Melting and boiling points , typically expressed in degrees Celsius at
30494-410: The relativistic spin–orbit interaction . The closeness in energy levels of the 5f, 6d, and 7s energy levels of thorium results in thorium almost always losing all four valence electrons and occurring in its highest possible oxidation state of +4. This is different from its lanthanide congener cerium, in which +4 is also the highest possible state, but +3 plays an important role and is more stable. Thorium
30687-919: The remaining 11 elements have half lives too short for them to have been present at the beginning of the Solar System, and are therefore considered transient elements. Of these 11 transient elements, five ( polonium , radon , radium , actinium , and protactinium ) are relatively common decay products of thorium and uranium . The remaining six transient elements (technetium, promethium, astatine, francium , neptunium , and plutonium ) occur only rarely, as products of rare decay modes or nuclear reaction processes involving uranium or other heavy elements. Elements with atomic numbers 1 through 82, except 43 (technetium) and 61 (promethium), each have at least one isotope for which no radioactive decay has been observed. Observationally stable isotopes of some elements (such as tungsten and lead ), however, are predicted to be slightly radioactive with very long half-lives: for example,
30880-494: The result of neutron activation of natural Th. Th (half-life 31 minutes) has not yet been observed in nature, but would be produced by the still-unobserved double beta decay of natural Ra. In deep seawaters the isotope Th makes up to 0.02% of natural thorium. This is because its parent U is soluble in water, but Th is insoluble and precipitates into the sediment. Uranium ores with low thorium concentrations can be purified to produce gram-sized thorium samples of which over
31073-458: The salt [Li(tmeda)] 3 [Th(CH 3 ) 7 ] (tmeda = (CH 3 ) 2 NCH 2 CH 2 N(CH 3 ) 2 ). Although one methyl group is only attached to the thorium atom (Th–C distance 257.1 pm) and the other six connect the lithium and thorium atoms (Th–C distances 265.5–276.5 pm), they behave equivalently in solution. Tetramethylthorium, Th(CH 3 ) 4 , is not known, but its adducts are stabilised by phosphine ligands. Th
31266-624: The same element can have different numbers of neutrons in their nuclei, known as isotopes of the element. Two or more atoms can combine to form molecules . Some elements are formed from molecules of identical atoms , e. g. atoms of hydrogen (H) form diatomic molecules (H 2 ). Chemical compounds are substances made of atoms of different elements; they can have molecular or non-molecular structure. Mixtures are materials containing different chemical substances; that means (in case of molecular substances) that they contain different types of molecules. Atoms of one element can be transformed into atoms of
31459-495: The same element having different numbers of neutrons are known as isotopes of the element. The number of protons in the nucleus also determines its electric charge , which in turn determines the number of electrons of the atom in its non-ionized state. The electrons are placed into atomic orbitals that determine the atom's chemical properties . The number of neutrons in a nucleus usually has very little effect on an element's chemical properties; except for hydrogen (for which
31652-404: The same number of protons in their nucleus), but having different numbers of neutrons . Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, said three isotopes are known as carbon-12 , carbon-13 , and carbon-14 ( C, C, and C). Natural carbon
31845-457: The second half of the 20th century, physics laboratories became able to produce elements with half-lives too short for an appreciable amount of them to exist at any time. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This practice can lead to the controversial question of which research group actually discovered an element, a question that delayed the naming of elements with atomic number of 104 and higher for
32038-545: The solutions of thorium salts are dominated by this cation. The Th ion is the largest of the tetrapositive actinide ions, and depending on the coordination number can have a radius between 0.95 and 1.14 Å. It is quite acidic due to its high charge, slightly stronger than sulfurous acid : thus it tends to undergo hydrolysis and polymerisation (though to a lesser extent than Fe ), predominantly to [Th 2 (OH) 2 ] in solutions with pH 3 or below, but in more alkaline solution polymerisation continues until
32231-401: The steel. At the very high cooling rates produced by quenching, the carbon has no time to migrate but is locked within the face-centred austenite and forms martensite . Martensite is a highly strained and stressed, supersaturated form of carbon and iron and is exceedingly hard but brittle. Depending on the carbon content, the martensitic phase takes different forms. Below 0.2% carbon, it takes on
32424-556: The steel. The early modern crucible steel industry resulted from the invention of Benjamin Huntsman in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots. The modern era in steelmaking began with the introduction of Henry Bessemer 's process in 1855, the raw material for which was pig iron. His method let him produce steel in large quantities cheaply, thus mild steel came to be used for most purposes for which wrought iron
32617-666: The strong nuclear force cannot overcome the electromagnetic repulsion between their protons. The alpha decay of Th initiates the 4 n decay chain which includes isotopes with a mass number divisible by 4 (hence the name; it is also called the thorium series after its progenitor). This chain of consecutive alpha and beta decays begins with the decay of Th to Ra and terminates at Pb. Any sample of thorium or its compounds contains traces of these daughters, which are isotopes of thallium , lead , bismuth, polonium, radon , radium , and actinium. Natural thorium samples can be chemically purified to extract useful daughter nuclides, such as Pb, which
32810-496: The synthetically produced transuranic elements, available samples have been too small to determine crystal structures. Chemical elements may also be categorized by their origin on Earth, with the first 94 considered naturally occurring, while those with atomic numbers beyond 94 have only been produced artificially via human-made nuclear reactions. Of the 94 naturally occurring elements, 83 are considered primordial and either stable or weakly radioactive. The longest-lived isotopes of
33003-955: The table to illustrate recurring trends in the properties of the elements. The layout of the table has been refined and extended over time as new elements have been discovered and new theoretical models have been developed to explain chemical behavior. Use of the periodic table is now ubiquitous in chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior. The table has also found wide application in physics , geology , biology , materials science , engineering , agriculture , medicine , nutrition , environmental health , and astronomy . Its principles are especially important in chemical engineering . The various chemical elements are formally identified by their unique atomic numbers, their accepted names, and their chemical symbols . The known elements have atomic numbers from 1 to 118, conventionally presented as Arabic numerals . Since
33196-555: The technology of that time, such qualities were produced by chance rather than by design. Natural wind was used where the soil containing iron was heated by the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons of soil, a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists were able to produce steel as the ancients did. Crucible steel , formed by slowly heating and cooling pure iron and carbon (typically in
33389-550: The temperature of dry ice , or by reacting thorium tetrafluoride with MgC 8 H 8 . It is unstable in air and decomposes in water or at 190 °C. Half sandwich compounds are also known, such as (η-C 8 H 8 )ThCl 2 (THF) 2 , which has a piano-stool structure and is made by reacting thorocene with thorium tetrachloride in tetrahydrofuran. The simplest of the cyclopentadienyls are Th(C 5 H 5 ) 3 and Th(C 5 H 5 ) 4 : many derivatives are known. The former (which has two forms, one purple and one green)
33582-544: The tetrahalides are all 8-coordinated hygroscopic compounds that dissolve easily in polar solvents such as water. Many related polyhalide ions are also known. Thorium tetrafluoride has a monoclinic crystal structure like those of zirconium tetrafluoride and hafnium tetrafluoride , where the Th ions are coordinated with F ions in somewhat distorted square antiprisms . The other tetrahalides instead have dodecahedral geometry. Lower iodides ThI 3 (black) and ThI 2 (gold-coloured) can also be prepared by reducing
33775-971: The tetraiodide with thorium metal: they do not contain Th(III) and Th(II), but instead contain Th and could be more clearly formulated as electride compounds. Many polynary halides with the alkali metals, barium , thallium, and ammonium are known for thorium fluorides, chlorides, and bromides. For example, when treated with potassium fluoride and hydrofluoric acid , Th forms the complex anion [ThF 6 ] (hexafluorothorate(IV)), which precipitates as an insoluble salt, K 2 [ThF 6 ] (potassium hexafluorothorate(IV)). Thorium borides, carbides, silicides, and nitrides are refractory materials, like those of uranium and plutonium, and have thus received attention as possible nuclear fuels . All four heavier pnictogens ( phosphorus , arsenic , antimony , and bismuth) also form binary thorium compounds. Thorium germanides are also known. Thorium reacts with hydrogen to form
33968-477: The thorium hydrides ThH 2 and Th 4 H 15 , the latter of which is superconducting below 7.5–8 K; at standard temperature and pressure, it conducts electricity like a metal. The hydrides are thermally unstable and readily decompose upon exposure to air or moisture. In an acidic aqueous solution, thorium occurs as the tetrapositive aqua ion [Th(H 2 O) 9 ] , which has tricapped trigonal prismatic molecular geometry : at pH < 3,
34161-420: The thorium–oxygen mass ratio of thorium oxide was 7.5 (its actual value is close to that, ~7.3), but he assumed the new element was divalent rather than tetravalent, and so calculated that the atomic mass was 7.5 times that of oxygen (120 amu ); it is actually 15 times as large. He determined that thorium was a very electropositive metal, ahead of cerium and behind zirconium in electropositivity. Metallic thorium
34354-430: The time of the Earth's formation, K and U contributed much more by virtue of their short half-lives, but they have decayed more quickly, leaving the contribution from Th and U predominant.) Its decay accounts for a gradual decrease of thorium content of the Earth: the planet currently has around 85% of the amount present at the formation of the Earth. The other natural thorium isotopes are much shorter-lived; of them, only Th
34547-457: The trivalent lanthanides which have similar ionic radii . Because of thorium's radioactivity, minerals containing it are often metamict (amorphous), their crystal structure having been damaged by the alpha radiation produced by thorium. An extreme example is ekanite , (Ca,Fe,Pb) 2 (Th,U)Si 8 O 20 , which almost never occurs in nonmetamict form due to the thorium it contains. Monazite (chiefly phosphates of various rare-earth elements)
34740-413: The two nuclides beyond bismuth (the other being U ) that have half-lives measured in billions of years; its half-life is 14.05 billion years, about three times the age of the Earth , and slightly longer than the age of the universe . Four-fifths of the thorium present at Earth's formation has survived to the present. Th is the only isotope of thorium occurring in quantity in nature. Its stability
34933-615: The universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made. The first 94 elements have been detected directly on Earth as primordial nuclides present from the formation of the Solar System , or as naturally occurring fission or transmutation products of uranium and thorium. The remaining 24 heavier elements, not found today either on Earth or in astronomical spectra, have been produced artificially: all are radioactive, with short half-lives; if any of these elements were present at
35126-522: The upper carbon content of steel, beyond which is cast iron. When carbon moves out of solution with iron, it forms a very hard, but brittle material called cementite (Fe 3 C). When steels with exactly 0.8% carbon (known as a eutectoid steel), are cooled, the austenitic phase (FCC) of the mixture attempts to revert to the ferrite phase (BCC). The carbon no longer fits within the FCC austenite structure, resulting in an excess of carbon. One way for carbon to leave
35319-528: The work of Dmitri Mendeleev , a Russian chemist who published the first recognizable periodic table in 1869. This table organizes the elements by increasing atomic number into rows (" periods ") in which the columns (" groups ") share recurring ("periodic") physical and chemical properties . The periodic table summarizes various properties of the elements, allowing chemists to derive relationships between them and to make predictions about elements not yet discovered, and potential new compounds. By November 2016,
35512-697: Was developed in Southern India and Sri Lanka in the 1st millennium BCE. Metal production sites in Sri Lanka employed wind furnaces driven by the monsoon winds, capable of producing high-carbon steel. Large-scale wootz steel production in India using crucibles occurred by the sixth century BC, the pioneering precursor to modern steel production and metallurgy. High-carbon steel was produced in Britain at Broxmouth Hillfort from 490–375 BC, and ultrahigh-carbon steel
35705-462: Was discovered in 1828 its first application dates only from 1885, when Austrian chemist Carl Auer von Welsbach invented the gas mantle , a portable source of light which produces light from the incandescence of thorium oxide when heated by burning gaseous fuels. Many applications were subsequently found for thorium and its compounds, including ceramics, carbon arc lamps, heat-resistant crucibles, and as catalysts for industrial chemical reactions such as
35898-603: Was discovered in 1903. The newly discovered phenomenon of radioactivity excited scientists and the general public alike. In the 1920s, thorium's radioactivity was promoted as a cure for rheumatism , diabetes , and sexual impotence . In 1932, most of these uses were banned in the United States after a federal investigation into the health effects of radioactivity. 10,000 individuals in the United States had been injected with thorium during X-ray diagnosis; they were later found to suffer health issues such as leukaemia and abnormal chromosomes. Public interest in radioactivity had declined by
36091-502: Was formerly used. The Gilchrist-Thomas process (or basic Bessemer process ) was an improvement to the Bessemer process, made by lining the converter with a basic material to remove phosphorus. Another 19th-century steelmaking process was the Siemens-Martin process , which complemented the Bessemer process. It consisted of co-melting bar iron (or steel scrap) with pig iron. These methods of steel production were rendered obsolete by
36284-417: Was isolated for the first time in 1914 by Dutch entrepreneurs Dirk Lely Jr. and Lodewijk Hamburger. In the periodic table published by Dmitri Mendeleev in 1869, thorium and the rare-earth elements were placed outside the main body of the table, at the end of each vertical period after the alkaline earth metals . This reflected the belief at that time that thorium and the rare-earth metals were divalent. With
36477-438: Was produced globally, with 630,000,000 tonnes (620,000,000 long tons; 690,000,000 short tons) recycled. Modern steels are made with varying combinations of alloy metals to fulfil many purposes. Carbon steel , composed simply of iron and carbon, accounts for 90% of steel production. Low alloy steel is alloyed with other elements, usually molybdenum , manganese, chromium, or nickel, in amounts of up to 10% by weight to improve
36670-729: Was produced in the Netherlands from the 2nd-4th centuries AD. The Roman author Horace identifies steel weapons such as the falcata in the Iberian Peninsula , while Noric steel was used by the Roman military . The Chinese of the Warring States period (403–221 BC) had quench-hardened steel, while Chinese of the Han dynasty (202 BC—AD 220) created steel by melting together wrought iron with cast iron, thus producing
36863-439: Was realised that the actinides were indeed filling f-orbitals rather than d-orbitals, with the transition-metal-like chemistry of the early actinides being the exception and not the rule. In 1945, when American physicist Glenn T. Seaborg and his team had discovered the transuranic elements americium and curium, he proposed the actinide concept , realising that thorium was the second member of an f-block actinide series analogous to
37056-631: Was the first known example of coordination number 11, the oxalate tetrahydrate has coordination number 10, and the borohydride (first prepared in the Manhattan Project ) has coordination number 14. These thorium salts are known for their high solubility in water and polar organic solvents. Many other inorganic thorium compounds with polyatomic anions are known, such as the perchlorates , sulfates , sulfites , nitrates, carbonates, phosphates , vanadates , molybdates , and chromates , and their hydrated forms. They are important in thorium purification and
37249-492: Was widely acknowledged during the first decades of the 20th century. In the second half of the century, thorium was replaced in many uses due to concerns about its radioactivity. Thorium is still being used as an alloying element in TIG welding electrodes but is slowly being replaced in the field with different compositions. It was also material in high-end optics and scientific instrumentation, used in some broadcast vacuum tubes, and as
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