Lawrencium

General properties
Name, symbol, number	lawrencium, Lr, 103
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(262)
Electron configuration	[Rn] 7s2 5f14 7p1 2, 8, 18, 32, 32, 8, 3
History
Discovery	Lawrence Berkeley National Laboratory (1961)

Lawrencium is a radioactive synthetic chemical element with the symbol Lr (formerly Lw) and atomic number 103. In the periodic table of the elements, it is a period 7 d-block element and the last element of the actinide series. Chemistry experiments have confirmed that lawrencium behaves as the heavier homologue to lutetium and is chemically similar to other actinides.

Lawrencium was first synthesized by the nuclear-physics team led by Albert Ghiorso on February 14, 1961, at the Lawrence Berkeley National Laboratory of the University of California. The first atoms of lawrencium were produced by bombarding a three-milligram target consisting of three isotopes of the element californium with boron-10 and boron-11 nuclei from the Heavy Ion Linear Accelerator. The team suggested the name lawrencium, and the symbol "Lw", but IUPAC changed the symbol to "Lr" in 1963. It was the last element of the actinide series to be produced.

All isotopes of lawrencium are radioactive; its most stable known isotope is lawrencium-262, with a half-life of approximately 3.6 hours. All its isotopes except for lawrencium-260, -261 and -262 decay with a half-life of less than a minute.

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Nobelium

General properties
Name, symbol, number	nobelium, No, 102
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(259)
Electron configuration	[Rn] 5f14 7s2 2, 8, 18, 32, 31, 8, 2
History
Discovery	Joint Institute for Nuclear Research (1966)

Nobelium is a synthetic element with the symbol No and atomic number 102. It was first correctly identified in 1966 by scientists at the Flerov Laboratory of Nuclear Reactions in Dubna, Soviet Union. Little is known about the element but limited chemical experiments have shown that it forms a stable divalent ion in solution as well as the predicted trivalent ion that is associated with its presence as one of the actinides.

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Mendelevium

General properties
Name, symbol, number	mendelevium, Md, 101
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(258)
Electron configuration	[Rn] 5f13 7s2 2, 8, 18, 32, 31, 8, 2
History
Discovery	Lawrence Berkeley National Laboratory (1955)

Mendelevium is a synthetic element with the symbol Md(formerly Mv) and the atomic number 101. A metallic radioactive transuranic element in the actinide series, mendelevium is usually synthesized by bombarding einsteinium with alpha particles. It was named after Dmitri Ivanovich Mendeleev, who created the Periodic Table. Mendeleev's periodic system is the fundamental way to classify all the chemical elements. The name "mendelevium" was accepted by the International Union of Pure and Applied Chemistry (IUPAC). On the other hand, the proposed symbol "Mv" submitted by the discoverers was not accepted, and IUPAC changed the symbol to "Md" in 1963.

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Fermium

General properties
Name, symbol, number	fermium, Fm, 100
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(257)
Electron configuration	[Rn] 5f12 7s2 2, 8, 18, 32, 30, 8, 2
History
Discovery	Lawrence Berkeley National Laboratory (1952)

Fermium is a synthetic element with symbol Fm and atomic number 100. It is a member of the actinide series. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared. A total of 19 isotopes are known, with ²⁵⁷Fm being the longest-lived one with a half-life of 100.5 days.

It was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Nobel laureate Enrico Fermi, one of the pioneers of nuclear physics. Its chemistry is typical of the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced fermium and its short half-life, there are currently no uses for it outside of basic scientific research. Like all synthetic elements, isotopes of fermium are extremely radioactive and are considered highly toxic.

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Einsteinium

General properties
Name, symbol, number	einsteinium, Es, 99
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(252)
Electron configuration	[Rn] 5f11 7s2 2, 8, 18, 32, 29, 8, 2
History
Discovery	Lawrence Berkeley National Laboratory (1952)

Einsteinium is a synthetic element with the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide.

Einsteinium was discovered as a component of the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein. Its most common isotope einsteinium-253 (half life 20.47 days) is produced artificially from decay of californium-253 in a few dedicated high-power nuclear reactors with a total yield on the order of one milligram per year. The reactor synthesis is followed by a complex procedure of separating einsteinium-253 from other actinides and products of their decay. Other isotopes are synthesized in various laboratories, but at much smaller amounts, by bombarding heavy actinide elements with light ions. Owing to the small amounts of produced einsteinium and the short half-life of its most easily produced isotope, there are currently almost no practical applications for it outside of basic scientific research. In particular, einsteinium was used to synthesize, for the first time, 17 atoms of the new element mendelevium in 1955.

Einsteinium is a soft, silvery, paramagnetic metal. Its chemistry is typical of the late actinides, with a preponderance of the +3 oxidation state; the +2 oxidation state is also accessible, especially in solids. The high radioactivity of einsteinium-253 produces a visible glow and rapidly damages its crystalline metal lattice, with released heat of about 1000 watts per gram. Difficulty in studying its properties is due to einsteinium-253's conversion to berkelium and then californium at a rate of about 3% per day. The isotope of einsteinium with the longest half life, einsteinium-252 (half life 471.7 days) would be more suitable for investigation of physical properties, but it has proven far more difficult to produce and is available only in minute quantities, and not in bulk. Einsteinium is the element with the highest atomic number which has been observed in macroscopic quantities in its pure form, and this was the common short-lived isotope einsteinium-253.

Like all synthetic transuranic elements, isotopes of einsteinium are extremely radioactive and are considered highly dangerous to health on ingestion.

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Californium

General properties
Name, symbol, number	californium, Cf, 98
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(251)
Electron configuration	[Rn] 5f10 7s2 2, 8, 18, 32, 28, 8, 2
History
Discovery	Lawrence Berkeley National Laboratory (1950)

Californium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made at the University of California, Berkeley in 1950 by bombarding curium with alpha particles (helium-4ions). It is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all the elements that have been produced in amounts large enough to see with the unaided eye (after einsteinium). The element was named after California and the University of California. It is the heaviest element to occur naturally on Earth; heavier elements can only be produced by synthesis.

Two crystalline forms exist for californium under normal pressure: one above 900 °C and one below 900 °C. A third form exists at high pressure. Californium slowly tarnishes in air at room temperature. Compounds of californium are dominated by a chemical form of the element, designated californium(III), that can participate in three chemical bonds. The most stable of californium's twenty known isotopes is californium-251, which has a half-life of 898 years. This short half-life means the element is not found in significant quantities in the Earth's crust. Californium-252, with a half-life of about 2.64 years, is the most common isotope used and is produced at the Oak Ridge National Laboratory in the United States and the Research Institute of Atomic Reactors in Russia.

Californium is one of the few transuranium elements that have practical applications. Most of these applications exploit the property of certain isotopes of californium to emit neutrons. For example, californium can be used to help start up nuclear reactors, and it is employed as a source of neutrons when studying materials with neutron diffraction and neutron spectroscopy. Californium can also be used in nuclear synthesis of higher mass elements; ununoctium (element 118) was synthesized by bombarding californium-249 atoms withcalcium-48 ions. Use of californium must take into account radiological concerns and the element's ability to disrupt the formation of red blood cells by bioaccumulating in skeletal tissue.

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Berkelium

General properties
Name, symbol, number	berkelium, Bk, 97
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(247)
Electron configuration	[Rn] 5f9 7s2 2, 8, 18, 32, 27, 8, 2
History
Discovery	Lawrence Berkeley National Laboratory (1949)

Berkelium is a transuranic radioactive chemical element with the symbol Bk and atomic number 97, a member of the actinide and transuranium element series. It is named after the city of Berkeley, California, the location of the University of California Radiation Laboratory where it was discovered in December 1949. This was the fifth transuranium element discovered after neptunium, plutonium, curium and americium.

The major isotope of berkelium, berkelium-249, is synthesized in minute quantities in dedicated high-flux nuclear reactors, mainly at the Oak Ridge National Laboratory in Tennessee, USA, and at the Research Institute of Atomic Reactors in Dimitrovgrad, Russia. The production of the second-important isotope berkelium-247 involves the irradiation of the rare isotope curium-244 with high-energy alpha particles.

Just over one gram of berkelium has been produced in the United States since 1967. There is no practical application of berkelium outside of scientific research which is mostly directed at the synthesis of heavier transuranic elements and transactinides. A 22 milligram batch of berkelium-249 was prepared during a 250-day irradiation period and then purified for a further 90 days at Oak Ridge in 2009. This sample was used to synthesize the element ununseptium for the first time in 2009 at the Joint Institute for Nuclear Research, Russia, after it was bombarded withcalcium-48 ions for 150 days. This was a culmination of the Russia–US collaboration on the synthesis of elements 113 to 118.

Berkelium is a soft, silvery-white, radioactive metal. The berkelium-249 isotope emits low-energy electrons and thus is relatively safe to handle. However, it decays with a half-life of 330 days to californium-249, which is a strong and hazardous emitter of alpha particles. This gradual transformation is an important consideration when studying the properties of elemental berkelium and its chemical compounds, since the formation of californium brings not only chemical contamination, but also self-radiation damage, and self-heating from the emitted alpha particles.

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Curium

General properties
Name, symbol, number	curium, Cm, 96
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(247)
Electron configuration	[Rn] 5f7 6d1 7s2 2, 8, 18, 32, 25, 9, 2
History
Discovery	Glenn T. Seaborg, Ralph A. James, Albert Ghiorso (1944)

Curium is a transuranic radioactive chemical element with the symbol Cm and atomic number 96. This element of the actinide series was named after Marie Skłodowska-Curie and her husband Pierre Curie - both were known for their research on radioactivity. Curium was first intentionally produced and identified in July 1944 by the group of Glenn T. Seaborg at the University of California, Berkeley. The discovery was kept secret and only released to the public in November 1945. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains about 20 grams of curium.

Curium is a hard, dense, silvery metal with a relatively high melting point and boiling point for an actinide. Whereas it is paramagnetic at ambient conditions, it becomes antiferromagnetic upon cooling, and other magnetic transitions are also observed for many curium compounds. In compounds, curium usually exhibits valence +3 and sometimes +4, and the +3 valence is predominant in solutions. Curium readily oxidizes, and its oxides are a dominant form of this element. It forms strongly fluorescent complexes with various organic compounds, but there is no evidence of its incorporation into bacteria and archaea. When introduced into the human body, curium accumulates in the bones, lungs and liver, where it promotes cancer.

All known isotopes of curium are radioactive and have a small critical mass for a sustained nuclear chain reaction. They predominantly emit α-particles, and the heat released in this process can potentially produce electricity in radioisotope thermoelectric generators. This application is hindered by the scarcity, high cost and radioactivity of curium isotopes. Curium is used in production of heavier actinides and of the ²³⁸Pu radionuclide for power sources inartificial pacemakers. It served as the α-source in the alpha particle X-ray spectrometers installed on the Sojourner, Mars, Mars 96, Athena, Spirit and Opportunity rovers as well as the Mars Science Laboratory to analyze the composition and structure of the rocks on the surface of Mars and the Moon. Such a spectrometer will also be used by the Philae lander of the Rosetta spacecraft to probe the surface of the 67P/Churyumov-Gerasimenko comet.

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Americium

General properties
Name, symbol, number	americium, Am, 95
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(243)
Electron configuration	[Rn] 5f7 7s2 2, 8, 18, 32, 25, 8, 2
History
Discovery	Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso (1944)

Americium is a transuranic radioactive chemical element that has the symbol Am and atomic number 95. This transuranic element of the actinide series is located in the periodic table below the lanthanide element europium, and thus by analogy was named after another continent, America.

Americium was first produced in 1944 by the group of Glenn T. Seaborg at the University of California, Berkeley. Although it is the third element in the transuranic series, it was discovered fourth, after the heavier curium. The discovery was kept secret and only released to the public in November 1945. Most americium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains about 100 grams of americium. It is widely used in commercial ionization chamber smoke detectors, as well as in neutron sources and industrial gauges. Several unusual applications, such as a nuclear battery or fuel for space ships with nuclear propulsion, have been proposed for the isotope ^242mAm, but they are as yet hindered by the scarcity and high price of this nuclear isomer.

Americium is a relatively soft radioactive metal with silvery appearance. Its most common isotopes are ²⁴¹Am and ²⁴³Am. In chemical compounds, they usually assume the oxidation state +3, especially in solutions. Several other oxidation states are known, which range from +2 to +7 and can be identified by their characteristic optical absorption spectra. The crystal lattice of solid americium and its compounds contains intrinsic defects, which are induced by self-irradiation with alpha particles and accumulate with time; this results in a drift of some material properties.

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Plutonium

General properties
Name, symbol, number	plutonium, Pu, 94
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(244)
Electron configuration	[Rn] 5f6 7s2 2, 8, 18, 32, 24, 8, 2
History
Discovery	Glenn T. Seaborg, Arthur Wahl, Joseph W. Kennedy, Edwin McMillan (1940–1)

Plutonium is a transuranic radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen, and silicon. When exposed to moist air, it forms oxides and hydrides that expand the sample up to 70% in volume, which in turn flake off as a powder that can spontaneously ignite. It is also radioactive and can accumulate in the bones. These properties make the handling of plutonium dangerous.

Plutonium is the heaviest primordial element by virtue of its most stable isotope, plutonium-244, whose half-life of about 80 million years is just long enough for the element to be found in trace quantities in nature. Plutonium is mostly a byproduct of nuclear fission in reactors where some of the neutrons released by the fission process convert uranium-238 nuclei into plutonium.

One utilized isotope of plutonium is plutonium-239, which has a half-life of 24,100 years. Plutonium-239 and plutonium-241 are both fissile, meaning the nuclei of their atoms can split when bombarded by thermal neutrons, releasing energy, gamma radiation and more neutrons. These neutrons can sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors.

Plutonium-238 has a half-life of 88 years and emits alpha particles. It is a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft.Plutonium-240 exhibits a high rate of spontaneous fission, raising the neutron flux of any sample containing it. The presence of plutonium-240 limits a sample's usability for weapons or reactor fuel, and determines its grade. Plutonium isotopes are expensive and inconvenient to separate, so particular isotopes are usually manufactured in specialized reactors.

A team led by Glenn T. Seaborg and Edwin McMillan at the University of California, Berkeley laboratory first synthesized plutonium in 1940 by bombardinguranium-238 with deuterons. Trace amounts of plutonium were subsequently discovered in nature. Producing plutonium in useful quantities for the first time was a major part of the Manhattan Project during World War II, which developed the first atomic bombs. The first nuclear test, "Trinity" (July 1945), and the second atomic bomb used to destroy a city (Nagasaki, Japan, in August 1945), "Fat Man", both had cores of plutonium-239. Human radiation experiments studying plutonium were conducted without informed consent, and a number of criticality accidents, some lethal, occurred during and after the war. Disposal of plutonium waste from nuclear power plants and dismantled nuclear weapons built during the Cold War is a nuclear-proliferation and environmental concern. Other sources of plutonium in the environment are fallout from numerous above-ground nuclear tests (now banned).

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Neptunium

General properties
Name, symbol, number	neptunium, Np, 93
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(237)
Electron configuration	[Rn] 5f4 6d1 7s2 2, 8, 18, 32, 22, 9, 2
History
Discovery	Edwin McMillan and Philip H. Abelson (1940)

Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive metal, neptunium is the first transuranic element, and belongs to the actinide series. Its most stable isotope, ²³⁷Np, is a by-product of nuclear reactors and plutonium production, and it can be used as a component in neutron detection equipment. Neptunium is also found in trace amounts in uranium ores due to transmutation reactions.

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Uranium

General properties
Name, symbol, number	uranium, U, 92
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	238.02891(3)
Electron configuration	[Rn] 5f3 6d1 7s2 2, 8, 18, 32, 21, 9, 2
History
Discovery	Martin Heinrich Klaproth (1789)
First isolation	Eugène-Melchior Péligot (1841)

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with symbol U and atomic number 92. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all its isotopes are unstable. The most common isotopes of uranium are uranium-238(which has 146 neutrons) and uranium-235 (which has 143 neutrons). Uranium has the second highest atomic weight of the primordially occurring elements, lighter only than plutonium. Its density is about 70% higher than that of lead, but not as dense as gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.

In nature, uranium is found as uranium-238 (99.2739–99.2752%), uranium-235 (0.7198–0.7202%), and a very small amount of uranium-234 (0.0050–0.0059%). Uranium decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion years and that of uranium-235 is 704 million years, making them useful in dating the age of the Earth.

Many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 has the distinction of being the only naturally occurring fissile isotope. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology. While uranium-238 has a small probability for spontaneous fission or even induced fission with fast neutrons, uranium-235 and to a lesser degree uranium-233 have a much higher fission cross-section for slow neutrons. In sufficient concentration, these isotopes maintain a sustained nuclear chain reaction. This generates the heat in nuclear power reactors, and produces the fissile material for nuclear weapons. Depleted uranium(²³⁸U) is used in kinetic energy penetrators and armor plating.

Uranium is used as a colorant in uranium glass, producing orange-red to lemon yellow hues. It was also used for tinting and shading in early photography. The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the planet Uranus. Eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by Antoine Becquerel. Research by Enrico Fermi and others starting in 1934 led to its use as a fuel in the nuclear power industry and in Little Boy, the first nuclear weapon used in war. An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived plutonium-239. The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is an ongoing concern for public health and safety. See Nuclear proliferation.

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Protactinium

General properties
Name, symbol, number	protactinium, Pa, 91
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	231.03588
Electron configuration	[Rn] 5f2 6d1 7s2 2, 8, 18, 32, 20, 9, 2
History
Prediction	Dmitri Mendeleev (1869)
Discovery	William Crookes (1900)
First isolation	William Crookes (1900)
Named by	Otto Hahn and Lise Meitner (1917–8)

Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states. The average concentrations of protactinium in the Earth's crust is typically on the order of a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Because of the scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside of scientific research, and for this purpose, protactinium is mostly extracted from spent nuclear fuel.

Protactinium was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and named brevium because of the short half-life of the specific isotope studied, namely protactinium-234. A more stable isotope (²³¹Pa) of protactinium was discovered in 1917/18 by Otto Hahn and Lise Meitner, and they choose the name proto-actinium, but then the IUPAC named it finally protactinium in 1949 and confirmed Hahn and Meitner as discoverers. The new name meant "parent of actinium" and reflected the fact that actinium is a product of radioactive decay of protactinium.

The longest-lived and most abundant (nearly 100%) naturally occurring isotope of protactinium, protactinium-231, has a half-life of 32,760 years and is a decay product of uranium-235. Much smaller trace amounts of the short-lived nuclear isomerprotactinium-234m occur in the decay chain of uranium-238. Protactinium-233 results from the decay of thorium-233 as part of the chain of events used to produce uranium-233 by neutron irradiation of thorium-232. It is an undesired intermediate product in thorium-based nuclear reactors and is therefore removed from the active zone of the reactor during the breeding process. Analysis of the relative concentrations of various uranium, thorium and protactinium isotopes in water and minerals is used in radiometric dating of sediments which are up to 175,000 years old and in modeling of various geological processes.

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Thorium

General properties
Name, symbol, number	thorium, Th, 90
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	232.03806
Electron configuration	[Rn] 6d2 7s2 2, 8, 18, 32, 18, 10, 2
History
Discovery	Jöns Jakob Berzelius (1829)

Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 by the Norwegian mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius and named after Thor, the Norse god of thunder.

In nature, virtually all thorium is found as thorium-232, which undergoes alpha decay with a half-life of about 14.05 billion years. Other isotopes of thorium are short-lived intermediates in the decay chains of higher elements, and only found in trace amounts. Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals.

Thorium was once commonly used as the light source in gas mantles and as an alloying material, but these applications have declined due to concerns about its radioactivity. Thorium is also used as an alloying element in nonconsumable TIG welding electrodes.

Canada, Germany, India, the Netherlands, the United Kingdom and the United States have experimented with using thorium as a substitute nuclear fuel in nuclear reactors. There is a growing interest in developing a thorium fuel cycle due to its safety benefits, absence of non-fertile isotopes, and its higher occurrence and availability when compared to uranium. India's three stage nuclear power programme is possibly the most well known and well funded of such efforts.

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Actinium

General properties
Name, symbol, number	actinium, Ac, 89
Element category	actinide
Group, period, block	n/a, 7, f
Standard atomic weight	(227)
Electron configuration	[Rn] 6d1 7s2 2, 8, 18, 32, 18, 9, 2
History
Discovery	André-Louis Debierne (1899)
First isolation	André-Louis Debierne (1899)

Actinium is a radioactive chemical element with symbol Ac (not to be confused with the abbreviation for an acetyl group) and has the atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table.

A soft, silvery-white radioactive metal, actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that prevents further oxidation. As with most lanthanides and actinides, actinium assumes oxidation state +3 in nearly all its chemical compounds. Actinium is found only in traces in uranium ores as the isotope ²²⁷Ac, which decays with a half-life of 21.772 years, predominantly emitting beta particles. One tonne of uranium ore contains about 0.2 milligrams of actinium. The close similarity of physical and chemical properties of actinium and lanthanum makes separation of actinium from the ore impractical. Instead, the element is prepared, in milligram amounts, by the neutron irradiation of ²²⁶Ra in a nuclear reactor. Owing to its scarcity, high price and radioactivity, actinium has no significant industrial use. Its current applications include a neutron source and an agent for radiation therapy targeting cancer cells in the body.

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Lutetium

General properties
Name, symbol, number	lutetium, Lu, 71
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	174.9668(4)
Electron configuration	[Xe] 6s2 4f14 5d1 2, 8, 18, 32, 9, 2
History
Discovery	Georges Urbain and Carl Auer von Welsbach (1906)
First isolation	Carl Auer von Welsbach (1906)

Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal which resists corrosion in dry, but not moist, air. It is the last element in the lanthanide series, and traditionally counted among the rare earths.

Lutetium was independently discovered in 1907 by French scientist Georges Urbain, Austrian mineralogist Baron Carl Auer von Welsbach, and American chemist Charles James. All of these men found lutetium as an impurity in the mineral ytterbia, which was previously thought to consist entirely of ytterbium. The dispute on the priority of the discovery occurred shortly after, with Urbain and von Welsbach accusing each other of publishing results influenced by the published research of the other; the naming honor went to Urbain as he published his results earlier. He chose the name lutecium for the new element but in 1949 the spelling of element 71 was changed to lutetium. In 1909, the priority was finally granted to Urbain and his names were adopted as official ones; however, the name cassiopeium (or later cassiopium) for element 71 proposed by von Welsbach was used by many German scientists until the 1950s.

Lutetium is not a particularly abundant element, though significantly more common than silver in the earth's crust; it has few specific uses. Lutetium-176 is a relatively abundant (2.5%) radioactive isotope with a half-life of about 38 billion years, and so used to determine the age of meteorites. Lutetium usually occurs in association with the element yttrium and is sometimes used in metal alloys and as a catalyst in various chemical reactions. ¹⁷⁷Lu-DOTA-TATE is used for radionuclide therapy (see Nuclear medicine) on neuroendocrine tumours.

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Ytterbium

General properties
Name, symbol, number	ytterbium, Yb, 70
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	173.054(5)
Electron configuration	[Xe] 4f14 6s2 2, 8, 18, 32, 8, 2
History
Discovery	Jean Charles Galissard de Marignac (1878)
First isolation	Georges Urbain (1907)

Ytterbium is a chemical element with symbol Yb and atomic number 70. It is the fourteenth and penultimate element in the lanthanide series, or last element in the f-block, which is the basis of the relative stability of the +2 oxidation state. However, like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds. In aqueous solution, like compounds of other late lanthanides, soluble ytterbium compounds form complexes with nine water molecules. Because of its closed-shell electron configuration, its density and melting and boiling points differ from those of the other lanthanides.

In 1878, the Swiss chemist Jean Charles Galissard de Marignac separated in the rare earth "erbia" another independent component, which he called "ytterbia", for Ytterby, the village in Sweden near where he found the new component of erbium. He suspected that ytterbia was a compound of a new element that he called "ytterbium" (in total, four elements were named after the village, the others being yttrium, terbium and erbium). In 1907, the new earth "lutecia" was separated from ytterbia, from which the element "lutecium" (now lutetium) was extracted by Georges Urbain, Carl Auer von Welsbach, and Charles James. After some discussion, Marignac's name "ytterbium" was retained. A relatively pure sample of the metal was obtained only in 1953. At present, ytterbium is mainly used as a dopant of stainless steel or active laser media, and less often as a gamma ray source.

Natural ytterbium is a mixture of seven stable isotopes, which altogether are present at concentrations of 3 parts per million. This element is mined in China, the United States, Brazil, and India in form of the minerals monazite, euxenite, and xenotime. The ytterbium concentration is low, because the element is found among many other rare earth elements; moreover, it is among the least abundant ones. Once extracted and prepared, ytterbium is somewhat hazardous as an eye and skin irritant. The metal is a fire and explosion hazard.

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Thullium

General properties
Name, symbol, number	thulium, Tm, 69
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	168.93421
Electron configuration	[Xe] 4f13 6s2 2, 8, 18, 31, 8, 2
History
Discovery	Per Teodor Cleve (1879)
First isolation	Per Teodor Cleve (1879)

Thullium is a chemical element that has the symbol Tm and atomic number 69. Thulium is the second least abundant of the lanthanides(promethium is only found in trace quantities on Earth). It is an easily workable metal with a bright silvery-gray luster. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices and in solid-state lasers.

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Erbium

General properties
Name, symbol, number	erbium, Er, 68
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	167.259
Electron configuration	[Xe] 4f12 6s2 2, 8, 18, 30, 8, 2
History
Discovery	Carl Gustaf Mosander (1842)

Erbium is a chemical element in the lanthanide series, with the symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements on Earth. As such, it is a rare earth element which is associated with several other rare elements in the mineral gadolinite from Ytterby in Sweden.

Erbium's principal uses involve its pink-colored Er³⁺ ions, which have optical fluorescent properties particularly useful in certain laser applications. Erbium-doped glasses or crystals can be used as optical amplification media, where erbium (III) ions are optically pumped at around 980 nm or 1480 nm and then radiate light at 1530 nm in stimulated emission. This process results in an unusually mechanically simple laser optical amplifier for signals transmitted by fiber optics. The 1550 nm wavelength is especially important for optical communications because standard single mode optical fibers have minimal loss at this particular wavelength. In addition to optical fiber lasers, a large variety of medical applications (i.e. dermatology, dentistry) utilize the erbium ion's 2940 nm emission (see Er:YAG laser), which is highly absorbed in water in tissues, making its effect very superficial. Such shallow tissue deposition of laser energy is helpful in laser surgery, and for the efficient production of steam for laser enamel ablation in certain types of laser dentistry.

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Holmium

General properties
Name, symbol, number	holmium, Ho, 67
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	164.93032
Electron configuration	[Xe] 4f11 6s2 2, 8, 18, 29, 8, 2
History
Discovery	Marc Delafontaine (1878)

Holmium is a chemical element with the symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare earth element. Holmium was discovered by Swedish chemist Per Theodor Cleve. Its oxide was first isolated from rare earth ores in 1878 and the element was named after the city of Stockholm.

Elemental holmium is a relatively soft and malleable silvery-white metal. It is too reactive to be found uncombined in nature, but when isolated, is relatively stable in dry air at room temperature. However, it reacts with water and rusts readily, and will also burn in air when heated.

Holmium is found in the minerals monazite and gadolinite, and is usually commercially extracted from monazite using ion exchange techniques. Its compounds in nature, and in nearly all of its laboratory chemistry, are trivalently oxidized, containing Ho(III) ions. Trivalent holmium ions have fluorescent properties similar to many other rare earth ions (while yielding their own set of unique emission light lines), and holmium ions are thus used in the same way as some other rare earths in certain laser and glass colorant applications.

Holmium has the highest magnetic strength of any element and therefore is used for the polepieces of the strongest static magnets. Because holmium strongly absorbs neutrons, it is also used in nuclear control rods.

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Dysprosium

General properties
Name, symbol, number	dysprosium, Dy, 66
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	162.500
Electron configuration	[Xe] 4f10 6s2 2, 8, 18, 28, 8, 2
History
Discovery	Lecoq de Boisbaudran (1886)

Dysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime. Naturally occurring dysprosium is composed of 7 isotopes, the most abundant of which is ¹⁶⁴Dy.

Dysprosium was first identified in 1886 by Paul Émile Lecoq de Boisbaudran, but was not isolated in pure form until the development of ion exchange techniques in the 1950s. Dysprosium is used for its high thermal neutron absorption cross-section in making control rods in nuclear reactors, for its high magnetic susceptibility in data storage applications, and as a component of Terfenol-D. Soluble dysprosium salts are mildly toxic, while the insoluble salts are considered non-toxic.

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Terbium

General properties
Name, symbol, number	terbium, Tb, 65
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	158.92535
Electron configuration	[Xe] 4f9 6s2 2, 8, 18, 27, 8, 2
History
Discovery	Carl Gustaf Mosander (1842)
First isolation	Carl Gustaf Mosander (1842)

Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime and euxenite.

Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate, materials that are used in solid-state devices, and as a crystal stabilizer of fuel cells which operate at elevated temperatures. As a component of Terfenol-D (an alloy that expands and contracts when exposed to magnetic fields more than any other alloy), terbium is of use in actuators, in naval sonar systems and in sensors.

Most of the world's terbium supply is used in "green" phosphors (which are usually yellow). Terbium oxide is in fluorescent lamps and TV tubes. Terbium "green" phosphors (which fluoresce a brilliant lemon-yellow) are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide "trichromatic" lighting technology, a high-efficiency white light used for standard illumination in indoor lighting.

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Gadolinium

General properties
Name, symbol, number	gadolinium, Gd, 64
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	157.25
Electron configuration	[Xe] 4f7 5d1 6s2 2, 8, 18, 25, 9, 2
History
Discovery	Jean Charles Galissard de Marignac (1880)
First isolation	Lecoq de Boisbaudran (1886)

Gadolinium is a chemical element with symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined (salt) form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with its discovery. It is named for gadolinite, one of the minerals in which it was found, in turn named for chemist Johan Gadolin. The metal was isolated by Lecoq de Boisbaudran in 1886.

Gadolinium metal possesses unusual metallurgic properties, to the extent that as little as 1% gadolinium can significantly improve the workability and resistance to high temperature oxidation of iron, chromium, and related alloys. Gadolinium as a metal or salt has exceptionally high absorption of neutrons and therefore is used for shielding in neutron radiography and in nuclear reactors. Like most rare earths, gadolinium forms trivalent ions which have fluorescent properties. Gd(III) salts have therefore been used as green phosphors in various applications.

The Gd(III) ion occurring in water-soluble salts is quite toxic to mammals. However, chelated Gd(III) compounds are far less toxic because they carry Gd(III) through the kidneys and out of the body before the free ion can be released into tissue. Because of its paramagnetic properties, solutions of chelated organic gadolinium complexes are used as intravenously administered gadolinium-based MRI contrast agents in medical magnetic resonance imaging. However, in a small minority of patients with renal failure, at least four such agents have been associated with development of the rare nodular inflammatory disease nephrogenic systemic fibrosis. This is thought to be due to the gadolinium ion itself, since Gd(III) carrier molecules associated with the disease differ.

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Europium

General properties
Name, symbol, number	europium, Eu, 63
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	151.964
Electron configuration	[Xe] 4f7 6s2 2, 8, 18, 25, 8, 2
History
Discovery	Eugène-Anatole Demarçay (1896)
First isolation	Eugène-Anatole Demarçay (1901)

Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard, silvery metal which readily oxidizes in air and water. Being a typical member of the lanthanide series, europium usually assumes the oxidation state +3, but the oxidation state +2 is also common: all europium compounds with oxidation state +2 are slightly reducing. Europium has no significant biological role and is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds.

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Samarium

General properties
Name, symbol, number	samarium, Sm, 62
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	150.36
Electron configuration	[Xe] 6s2 4f6 2, 8, 18, 24, 8, 2
History
Discovery	Lecoq de Boisbaudran (1879)
First isolation	Lecoq de Boisbaudran (1879)

Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3. Compounds of samarium (II) are also known, most notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as well as samarium(II) iodide. The last compound is a common reducing agent in chemical synthesis. Samarium has no significant biological role and is only slightly toxic.

Samarium was discovered in 1879 by the French chemist Paul Émile Lecoq de Boisbaudran and named after the mineral samarskite from which it was isolated. The mineral itself was earlier named after a Russian mine official, Colonel Vasili Samarsky-Bykhovets, who thereby became the first person to have a chemical element named after him, albeit indirectly. Although classified as a rare earth element, samarium is the 40th most abundant element in the Earth's crust and is more common than such metals as tin. Samarium occurs with concentration up to 2.8% in several minerals including cerite, gadolinite, samarskite, monazite and bastnäsite, the last two being the most common commercial sources of the element. These minerals are mostly found in China, the USA, Brazil, India, Sri Lanka and Australia; China is by far the world leader in samarium mining and production.

The major commercial application of samarium is in samarium-cobalt magnets which have permanent magnetization second only to neodymium magnets; however, samarium compounds can withstand significantly higher temperatures, above 700 °C, without losing their magnetic properties. The radioactive isotopesamarium-153 is the major component of the drug samarium (¹⁵³Sm) lexidronam (Quadramet) which kills cancer cells in the treatment of lung cancer, prostate cancer, breast cancer and osteosarcoma. Another isotope, samarium-149, is a strong neutron absorber and is therefore added to the control rods of nuclear reactors. It is also formed as a decay product during the reactor operation and is one of the important factors considered in the reactor design and operation. Other applications of samarium include catalysis of chemical reactions, radioactive dating and an X-ray laser.

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Promethium

General properties
Name, symbol, number	promethium, Pm, 61
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	[145]
Electron configuration	[Xe] 6s2 4f5 2, 8, 18, 23, 8, 2
History
Discovery	Chien Shiung Wu, Emilio Segrè, Hans Bethe (1942)
First isolation	Charles D. Coryell, Jacob A. Marinsky, Lawrence E. Glendenin, Harold G. Richter (1945)
Named by	Grace Mary Coryell (1945)

Promethium, originally prometheum, is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is one of only two such elements that are followed in the periodic table by elements with stable forms, a distinction shared with technetium. Chemically, promethium is a lanthanide, which forms salts when combined with other elements. Promethium shows only one stable oxidation state of +3; however, a few +2 compounds may exist.

In 1902, Bohuslav Brauner suggested there was an element with properties intermediate between those of the known elements neodymium (60) and samarium (62); this was confirmed in 1914 by Henry Moseley who, having measured the atomic numbers of all the elements then known, found there was no element with atomic number 61. In 1926, an Italian and an American group claimed to have isolated a sample of element 61; both "discoveries" were soon proven to be false. In 1938, during a nuclear experiment conducted at Ohio State University, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not generally recognized. Promethium was first produced and characterized at Oak Ridge National Laboratory in 1945 by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. The discoverers proposed the name "prometheum" (the spelling was subsequently changed), derived from Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans, to symbolize "both the daring and the possible misuse of mankind's intellect." However, a sample of the metal was made only in 1963.

There are two possible sources for natural promethium: rare decays of natural europium-151 (producing promethium-147), and uranium(various isotopes). Practical applications exist only for chemical compounds of promethium-147, which are used in luminous paint, atomic batteries and thickness measurement devices, even though promethium-145 is the most stable promethium isotope. Since natural promethium is exceedingly scarce, the element is typically synthesized by bombarding uranium-235 (enriched uranium) with thermal neutrons to produce promethium-147.

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Neodymium

General properties
Name, symbol, number	neodymium, Nd, 60
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	144.242
Electron configuration	[Xe] 4f4 6s2 2, 8, 18, 22, 8, 2
History
Discovery	Carl Auer von Welsbach (1885)

Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Although neodymium is classed as a "rare earth", it is no rarer than cobalt, nickel, and copper ore, and is widely distributed in the Earth's crust. Most of the world's neodymium is mined in China.

Neodymium compounds were first commercially used as glass dyes in 1927, and they remain a popular additive in glasses. The color of neodymium compounds—due to the Nd³⁺ ion—is often a reddish-purple but it changes with the type of lighting, due to fluorescent effects. Some neodymium-doped glasses are also used in lasers that emit infrared light with wavelengths between 1047 and 1062 nanometers. These have been used in extremely high power applications, such as experiments in inertial confinement fusion.

Another chief use of neodymium is as the free pure element. It is used as a component in the alloys used to make high-strength neodymium magnets – powerful permanent magnets. These magnets are widely used in such products as microphones, professional loudspeakers, in-ear headphones, and computer hard disks, where low magnet mass or volume, or strong magnetic fields are required. Larger neodymium magnets are used in high power versus weight electric motors (for example in hybrid cars) and generators (for example aircraft and wind turbine electric generators).

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Praseodymium

General properties
Name, symbol, number	praseodymium, Pr, 59
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	140.90765
Electron configuration	[Xe] 4f3 6s2 2, 8, 18, 21, 8, 2
History
Discovery	Carl Auer von Welsbach (1885)

Praseodymium is a chemical element that has the symbol Pr and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating.

The element was named for the color of its primary oxide. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare earth oxide residue he called "didymium" from a residue he called "lantana," in turn separated from cerium salts. In 1885, the Austrian chemist Baron Carl Auer von Welsbach separated didymium into two salts of different colors, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasios(πράσιος), meaning green, and didymos(δίδυμος), twin.

Like most rare earth elements, praseodymium most readily forms trivalent Pr (III) ions. These are yellow-green in water solution, and various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its use to filter yellow light from light sources.

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Cerium

General properties
Name, symbol, number	cerium, Ce, 58
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	140.116
Electron configuration	[Xe] 4f1 5d1 6s2 2, 8, 18, 19, 9, 2
History
Discovery	Martin Heinrich Klaproth, Jöns Jakob Berzelius, Wilhelm Hisinger (1803)
First isolation	Carl Gustaf Mosander (1839)

Cerium is a chemical element with symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet Ceres (itself named for the Roman goddess of agriculture). Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is found in a number of minerals, the most important being monazite and bastnasite. Commercial applications of cerium are numerous. They include catalysts, additives to fuel to reduce emissions and to glass and enamels to change their color. Cerium oxide is an important component of glass polishing powders and phosphors used in screens and fluorescent lamps. It is also used in the "flint" (actually ferrocerium) of lighters.

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Lanthanum

General properties
Name, symbol, number	lanthanum, La, 57
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	138.90547
Electron configuration	[Xe] 5d1 6s2 2, 8, 18, 18, 9, 2
History
Discovery	Carl Gustaf Mosander (1838)

Lanthanum is a chemical element with the symbol La and atomic number 57. Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and other rare earth elements. Lanthanum is a malleable, ductile, and soft metal that oxidizes rapidly when exposed to air. It is produced from the minerals monazite and bastnäsite using a complex multistage extraction process. Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon lighting for studio lighting and projection, ignition elements in lighters and torches, electron cathodes, scintillators, and others. Lanthanum carbonate (La₂(CO₃)₃) was approved as a medication against renal failure.

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Ununoctium

General properties
Name, symbol, number	ununoctium, Uuo, 118
Element category	unknown
Group, period, block	18, 7, p
Standard atomic weight	(294)
Electron configuration	[Rn] 5f14 6d10 7s2 7p6 (predicted) 2, 8, 18, 32, 32, 18, 8 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2002)

Ununoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is currently the only synthetic member of Group 18. It has the highest atomic number and highest atomic mass of all the elements discovered so far.

The radioactive ununoctium atom is very unstable, and since 2002, only three or possibly four atoms of the isotope ²⁹⁴Uuo have been detected. While this allowed for very little experimental characterization of its properties and possible compounds, theoretical calculations have resulted in many predictions, including some unexpected ones. For example, although ununoctium is a member of Group 18, it may possibly not be a noble gas, unlike all the other Group 18 elements. It was formerly thought to be a gas but is now predicted to be a solid under normal conditions due to relativistic effects.

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Ununseptium

General properties
Name, symbol, number	ununseptium, Uus, 117
Element category	unknown
Group, period, block	17, 7, p
Standard atomic weight	(294)
Electron configuration	[Rn] 5f14 6d10 7s2 7p5 (predicted) 2, 8, 18, 32, 32, 18, 7 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2010)

Ununseptium is the superheavy artificial chemical element with temporary symbol Uus and atomic number 117. The element, also known as eka-astatine or simply element 117, is the second-heaviest of all the elements that have been reportedly created so far and is the second-to-last element of the 7th period of the periodic table. Its discovery was first announced in 2010—synthesis was claimed in Dubna, Russia, by a joint Russian–American collaboration, thus making it the most recently discovered element. Another experiment in 2011 created one of its daughter isotopes directly, partially confirming the results of the discovery experiment, and the same experiment that was reportedly used to first synthesize the element was repeated successfully in 2012. However, the IUPAC/IUPAP Joint Working Party (JWP), which is in charge of examining claims of discovery of superheavy elements, has made no comment yet on whether the element can be recognized as discovered. Once it is so recognized, it may receive a permanent name which will be suggested for the element by the discoverers; "ununseptium" is a temporary systematic element name that is intended to be used before a permanent one is established. However, it is commonly called "element 117" by researchers and in the literature instead of "ununseptium".

In the periodic table, ununseptium is located in group 17, all previous members of which are halogens. However, the element is likely to have significantly different properties from the halogens, although a few key properties such as the melting and boiling points, as well as the first ionization energy are expected to follow the periodic trends. While scientists agree that lighter ununseptium isotopes are very unstable, there are signs that some heavier ununseptium isotopes may be much more stable.

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Livermorium

General properties
Name, symbol, number	livermorium, Lv, 116
Element category	unknown
Group, period, block	16, 7, p
Standard atomic weight	(293)
Electron configuration	[Rn] 5f14 6d10 7s2 7p4 (predicted) 2, 8, 18, 32, 32, 18, 6 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2000)

Livermorium is the synthetic superheavy element with the symbol Lv and atomic number 116. The name was adopted by IUPAC on May 31, 2012.

It is placed as the heaviest member of group 16 (VIA) although a sufficiently stable isotope is not known at this time to allow chemical experiments to confirm its position as a heavier homologue to polonium.

It was first detected in 2000. Since then, about 35 atoms of livermorium have been produced, either directly or as a decay product of ununoctium, belonging to the four neighbouring isotopes with masses 290–293. The most stable isotope known is livermorium-293 with a half-life of ~60 ms.

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Ununpentium

General properties
Name, symbol, number	ununpentium, Uup, 115
Element category	unknown
Group, period, block	15, 7, p
Standard atomic weight	(288)
Electron configuration	[Rn] 5f14 6d10 7s2 7p3 (predicted) 2, 8, 18, 32, 32, 18, 5 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2003)

Ununpentium is the temporary name of a synthetic superheavy element in the periodic table that has the temporary symbol Uup and has the atomic number 115.

It is placed as the heaviest member of group 15 (VA) although a sufficiently stable isotope is not known at this time that would allow chemical experiments to confirm its position as a heavier homologue to bismuth. It was first observed in 2003 and about 50 atoms of ununpentium have been synthesized to date, with about 25 direct decays of the parent element having been detected. Four consecutive isotopes are currently known, ^287–290Uup, with ²⁸⁹Uup having the longest measured half-life of ~200 ms.

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Flevorium

General properties
Name, symbol, number	flerovium, Fl, 114
Element category	unknown
Group, period, block	14, 7, p
Standard atomic weight	(289)
Electron configuration	[Rn] 5f14 6d10 7s2 7p2 (predicted) 2, 8, 18, 32, 32, 18, 4 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (1999)

Flevorium is the radioactive chemical element with the symbol Fl and atomic number 114. The element is named after Russian physicist Georgy Flyorov, the founder of the Joint Institute for Nuclear Research in Dubna, Russia, where the element was discovered. The name was adopted by IUPAC on May 30, 2012.

About 80 decays of atoms of flerovium have been observed to date, 50 directly and 30 from the decay of the heavier elements livermorium and ununoctium. All decays have been assigned to the five neighbouring isotopes with mass numbers 285–289. The longest-lived isotope currently known is ²⁸⁹Fl with a half-life of ~2.6 s, although there is evidence for a nuclear isomer, ^289bFl, with a half-life of ~66 s, that would be one of the longest-lived nuclei in the superheavy element region.

Chemical studies performed in 2007–2008 indicate that flerovium is unexpectedly volatile for a group 14 element; in preliminary results it even seemed to exhibit noble-gas-like properties due to relativistic effects.

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Ununtrium

General properties
Name, symbol, number	ununtrium, Uut, 113
Element category	unknown presumably post-transition metals
Group, period, block	13, 7, p
Standard atomic weight	(286)
Electron configuration	[Rn] 5f14 6d10 7s2 7p1 (predicted) 2, 8, 18, 32, 32, 18, 3 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2003)

Ununtrium is the temporary name of a chemical element with the temporary symbol Uut and atomic number 113. It is an extremely radioactive synthetic element (an element that can be created in a laboratory but is not found in nature); the most stable known isotope, ununtrium-286, has a half-life of 20 seconds. Ununtrium was first created in 2003 by the Joint Institute for Nuclear Research in Dubna, Russia.

In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in the boron group, although no chemical experiments have been carried out to confirm that it behaves as the heavier homologue to thallium in the boron group. Ununtrium is calculated to have some similar properties to its lighter homologues, boron, aluminium, gallium, indium, and thallium, although it should also show several major differences from them. Unlike all the other p-block elements, it is even predicted to show some transition metal character.

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Copernicium

General properties
Name, symbol, number	copernicium, Cn, 112
Element category	transition metal
Group, period, block	12, 7, d
Standard atomic weight	(285)
Electron configuration	[Rn] 5f14 6d10 7s2 (predicted) 2, 8, 18, 32, 32, 18, 2 (predicted)
History
Discovery	Gesellschaft für Schwerionenforschung (1996)

Copernicium is a chemical element with symbol Cn and atomic number 112. It is an extremely radioactive synthetic element that can only be created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 29 seconds, but it is possible that this copernicium isotope may have a nuclear isomer with a longer half-life, 8.9 min. Copernicium was first created in 1996 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the astronomer Nicolaus Copernicus.

In the periodic table of the elements, it is a d-block transactinide element. During reactions with gold, it has been shown to be an extremely volatile metal and a group 12 element, and it may even be a gas at standard temperature and pressure. Copernicium is calculated to have several properties that differ between it and its lighter homologues, zinc, cadmium and mercury; the most notable of them is withdrawing two 6d-electrons before 7s ones due to relativistic effects, which confirm copernicium as an undisputed transition metal. Copernicium is also calculated to show a predominance of the oxidation state +4, while mercury shows it in only one compound at extreme conditions and zinc and cadmium do not show it at all. It has also been predicted to be more difficult to oxidise copernicium from its neutral state than the other group 12 elements.

In total, approximately 75 atoms of copernicium have been detected using various nuclear reactions.

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Roentgenium

General properties
Name, symbol, number	roentgenium, Rg, 111
Element category	unknown but probably a transition metal
Group, period, block	11, 7, d
Standard atomic weight	(281)
Electron configuration	[Rn] 5f14 6d9 7s2 (predicted) 2, 8, 18, 32, 32, 17, 2 (predicted)
History
Discovery	Gesellschaft für Schwerionenforschung (1994)

Roentgenium is a chemical element with the symbol Rg and atomic number 111. It is an extremely radioactive synthetic element (an element that can be created in a laboratory but is not found in nature); the most stable known isotope, roentgenium-281, has a half-life of 26 seconds. Roentgenium was first created in 1994 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the physicist Wilhelm Röntgen (also spelled Roentgen).

In the periodic table, it is a d-block transactinide element. It is a member of the 7th period and is placed in the group 11 elements, although no chemical experiments have been carried out to confirm that it behaves as the heavier homologue to gold in group 11. Roentgenium is calculated to have similar properties to its lighter homologues, copper, silver, and gold, although it may show some differences from them.

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Darmstadtium

General properties
Name, symbol, number	darmstadtium, Ds, 110
Element category	unknown but probably a transition metal
Group, period, block	10, 7, d
Standard atomic weight	(281)
Electron configuration	[Rn] 5f14 6d8 7s2 (predicted) 2, 8, 18, 32, 32, 16, 2 (predicted)
History
Discovery	Gesellschaft für Schwerionenforschung (1994)

Darmstadtium is a chemical element with the symbol Ds and atomic number 110. It is an extremely radioactive synthetic element. The most stable known isotope, darmstadtium-281, has a half-life of approximately 11 seconds, but it is possible that this darmstadtium isotope may have an isomer with a longer half-life, 3.7 minutes. Darmstadtium was first created in 1994 by the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt-Arheilgen near Darmstadt, Germany. It was named after the city of Darmstadt, where it was discovered.

In the periodic table, it is a d-block transactinide element. It is a member of the 7th period and is placed in the group 10 elements, although no chemical experiments have yet been carried out to confirm that it behaves as the heavier homologue to platinum in group 10. Darmstadtium is calculated to have similar properties to its lighter homologues, nickel, palladium, and platinum.

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Meitnerium

General properties
Name, symbol, number	meitnerium, Mt, 109
Element category	unknown but probably a transition metal
Group, period, block	9, 7, d
Standard atomic weight	(278)
Electron configuration	[Rn] 5f14 6d7 7s2 (calculated) 2, 8, 18, 32, 32, 15, 2 (predicted)
History
Discovery	Gesellschaft für Schwerionenforschung (1982)

Meitnerium is a chemical element with the symbol Mt and atomic number 109. It is an extremely radioactive synthetic element (an element that can be created in a laboratory but is not found in nature); the most stable known isotope, meitnerium-278, has a half-life of 7.6 seconds. Meitnerium was first created in 1982 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the physicist Lise Meitner.

In the periodic table, it is a d-block transactinide element. It is a member of the 7th period and is placed in the group 9 elements, although no chemical experiments have been carried out to confirm that it behaves as the heavier homologue to iridium in group 9. Meitnerium is calculated to have similar properties to its lighter homologues, cobalt, rhodium, and iridium.

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