Technetium

Chemical element, symbol Tc and atomic number 43 / From Wikipedia, the free encyclopedia

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Technetium is a chemical element; it has symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. Technetium and promethium are the only radioactive elements whose neighbours in the sense of atomic number are both stable. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous fission product in uranium ore and thorium ore (the most common source), or the product of neutron capture in molybdenum ores. This silvery gray, crystalline transition metal lies between manganese and rhenium in group 7 of the periodic table, and its chemical properties are intermediate between those of both adjacent elements. The most common naturally occurring isotope is 99Tc, in traces only.

Quick facts: Technetium, Pronunciation, Appearance, Mass n...
Technetium, 43Tc
Technetium-sample-cropped.jpg
Technetium
Pronunciation/tɛkˈnʃ(i)əm/ (tek-NEE-sh(ee-)əm)
Appearanceshiny gray metal
Mass number[97]
Technetium in the periodic table
Mn

Tc

Re
molybdenumtechnetiumruthenium
Atomic number (Z)43
Groupgroup 7
Periodperiod 5
Block  d-block
Electron configuration[Kr] 4d5 5s2
Electrons per shell2, 8, 18, 13, 2
Physical properties
Phase at STPsolid
Melting point2430 K (2157 °C, 3915 °F)
Boiling point4538 K (4265 °C, 7709 °F)
Density (near r.t.)11 g/cm3
Heat of fusion33.29 kJ/mol
Heat of vaporization585.2 kJ/mol
Molar heat capacity24.27 J/(mol·K)
Vapor pressure (extrapolated)
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2727 2998 3324 3726 4234 4894
Atomic properties
Oxidation states−1, 0, +1,[1][citation needed] +2, +3, +4, +5, +6, +7 (a strongly acidic oxide)
ElectronegativityPauling scale: 1.9
Ionization energies
  • 1st: 686.9[2] kJ/mol
  • 2nd: 1470 kJ/mol
  • 3rd: 2850 kJ/mol
Atomic radiusempirical: 136 pm
Covalent radius147±7 pm
Van der Waals radius205 pm
Color lines in a spectral range
Spectral lines of technetium
Other properties
Natural occurrencefrom decay
Crystal structure hexagonal close-packed (hcp)
Hexagonal close packed crystal structure for technetium
Thermal expansion7.1 µm/(m⋅K)[3] (at r.t.)
Thermal conductivity50.6 W/(m⋅K)
Electrical resistivity200 nΩ⋅m (at 20 °C)
Magnetic orderingParamagnetic
Molar magnetic susceptibility+270.0×10−6 cm3/mol (298 K)[4]
Speed of sound thin rod16,200 m/s (at 20 °C)
CAS Number7440-26-8
History
PredictionDmitri Mendeleev (1871)
Discovery and first isolationEmilio Segrè and Carlo Perrier (1937)
Isotopes of technetium
Main isotopes[5] Decay
abun­dance half-life (t1/2) mode pro­duct
95mTc synth 61.96 d β+ 95Mo
IT 95Tc
96Tc synth 4.28 d β+ 96Mo
γ
97Tc synth 4.21×106 y ε 97Mo
97mTc synth 91.1 d IT 97Tc
ε ...
98Tc synth 4.2×106 y β 98Ru
β+
99Tc trace 2.111×105 y β 99Ru
99mTc synth 6.01 h IT 99Tc
β
Symbol_category_class.svg Category: Technetium
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Many of technetium's properties had been predicted by Dmitri Mendeleev before it was discovered. Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese (Em). In 1937, technetium (specifically the technetium-98 isotope) became the first predominantly artificial element to be produced, hence its name (from the Greek τεχνητός, technetos, from techne, as in "craft", "art" and having the meaning of "artificial", + -ium).

One short-lived gamma ray-emitting nuclear isomer, technetium-99m, is used in nuclear medicine for a wide variety of tests, such as bone cancer diagnoses. The ground state of the nuclide technetium-99 is used as a gamma-ray-free source of beta particles. Long-lived technetium isotopes produced commercially are byproducts of the fission of uranium-235 in nuclear reactors and are extracted from nuclear fuel rods. Because even the longest-lived isotope of technetium has a relatively short half-life (4.21 million years), the 1952 detection of technetium in red giants helped to prove that stars can produce heavier elements.

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