Technetium

Technetium, 43Tc
Technetium.jpg
Technetium
Pronunciationəm/ (NEE-shee-əm)
Appearanceshiny gray metal
Mass number[97]
Technetium in the periodic table
HydrogenHelium
LithiumBerylliumBoronCarbonNitrogenOxygenFluorineNeon
SodiumMagnesiumAluminiumSiliconPhosphorusSulfurChlorineArgon
PotassiumCalciumScandiumTitaniumVanadiumChromiumManganeseIronCobaltNickelCopperZincGalliumGermaniumArsenicSeleniumBromineKrypton
RubidiumStrontiumYttriumZirconiumNiobiumMolybdenumTechnetiumRutheniumRhodiumPalladiumSilverCadmiumIndiumTinAntimonyTelluriumIodineXenon
CaesiumBariumLanthanumCeriumPraseodymiumNeodymiumPromethiumSamariumEuropiumGadoliniumTerbiumDysprosiumHolmiumErbiumThuliumYtterbiumLutetiumHafniumTantalumTungstenRheniumOsmiumIridiumPlatinumGoldMercury (element)ThalliumLeadBismuthPoloniumAstatineRadon
FranciumRadiumActiniumThoriumProtactiniumUraniumNeptuniumPlutoniumAmericiumCuriumBerkeliumCaliforniumEinsteiniumFermiumMendeleviumNobeliumLawrenciumRutherfordiumDubniumSeaborgiumBohriumHassiumMeitneriumDarmstadtiumRoentgeniumCoperniciumNihoniumFleroviumMoscoviumLivermoriumTennessineOganesson
Mn

Tc

Re
molybdenumtechnetiumruthenium
Atomic number (Z)43
Groupgroup 7
Periodperiod 5
Blockd-block
Element category  Transition metal
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)1101001 k10 k100 k
at T (K)272729983324372642344894
Atomic properties
Oxidation states−3, −1, 0, +1,[1] +2, +3,[1] +4, +5, +6, +7 (a strongly acidic oxide)
ElectronegativityPauling scale: 1.9
Ionization energies
  • 1st: 702 kJ/mol
  • 2nd: 1470 kJ/mol
  • 3rd: 2850 kJ/mol
Atomic radiusempirical: 136 pm
Covalent radius147±7 pm
Color lines in a spectral range
Spectral lines of technetium
Other properties
Natural occurrencefrom decay
Crystal structurehexagonal close-packed (hcp)
Hexagonal close packed crystal structure for technetium
Speed of sound thin rod16,200 m/s (at 20 °C)
Thermal expansion7.1 µm/(m·K)[2] (at r.t.)
Thermal conductivity50.6 W/(m·K)
Electrical resistivity200 nΩ·m (at 20 °C)
Magnetic orderingParamagnetic
Magnetic susceptibility+270.0·10−6 cm3/mol (298 K)[3]
CAS Number7440-26-8
History
PredictionDmitri Mendeleev (1871)
Discovery and first isolationEmilio Segrè and Carlo Perrier (1937)
Main isotopes of technetium
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct
95mTcsyn61 dε95Mo
γ
IT95Tc
96Tcsyn4.3 dε96Mo
γ
97Tcsyn4.21×106 yε97Mo
97mTcsyn91 dIT97Tc
98Tcsyn4.2×106 yβ98Ru
γ
99Tctrace2.111×105 yβ99Ru
99mTcsyn6.01 hIT99Tc
γ
| references

Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive; none are stable other than the fully ionized state of 97Tc.[4] Nearly all technetium is produced as a synthetic element, and only about 18,000 tons are estimated to exist at any given time in the Earth's crust. 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 these two adjacent elements. The most common naturally occurring isotope is 99Tc.

Many of technetium's properties were predicted by Dmitri Mendeleev before the element 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-97 isotope) became the first predominantly artificial element to be produced, hence its name (from the Greek τεχνητός, meaning "synthetic or artificial", + -ium).

One short-lived gamma ray-emitting nuclear isomer of technetium—technetium-99m—is used in nuclear medicine for a wide variety of diagnostic tests, such as bone cancer diagnoses. The ground state of this nuclide, technetium-99, is used as a gamma-ray-free source of beta particles. Long-lived technetium isotopes produced commercially are by-products of the fission of uranium-235 in nuclear reactors and are extracted from nuclear fuel rods. Because no isotope of technetium has a half-life longer than 4.21 million years (technetium-97), the 1952 detection of technetium in red giants helped to prove that stars can produce heavier elements.

History

Search for element 43

From the 1860s through 1871, early forms of the periodic table proposed by Dmitri Mendeleev contained a gap between molybdenum (element 42) and ruthenium (element 44). In 1871, Mendeleev predicted this missing element would occupy the empty place below manganese and have similar chemical properties. Mendeleev gave it the provisional name ekamanganese (from eka-, the Sanskrit word for one) because the predicted element was one place down from the known element manganese.[5]

Early misidentifications

Many early researchers, both before and after the periodic table was published, were eager to be the first to discover and name the missing element. Its location in the table suggested that it should be easier to find than other undiscovered elements.

Year Claimant Suggested name Actual material
1828 Gottfried Osann Polinium Iridium
1846 R. Hermann Ilmenium Niobium-tantalum alloy
1847 Heinrich Rose Pelopium[6] Niobium-tantalum alloy
1877 Serge Kern Davyum Iridium-rhodium-iron alloy
1896 Prosper Barrière Lucium Yttrium
1908 Masataka Ogawa Nipponium Rhenium, which was the then unknown dvi-manganese[7]

Irreproducible results

Periodisches System der Elemente (1904–1945, now at the Gdańsk University of Technology): lack of elements: 84 polonium Po (though discovered as early as in 1898 by Maria Sklodowska-Curie), 85 astatine At (1940, in Berkeley), 87 francium Fr (1939, in France), 93 neptunium Np (1940, in Berkeley) and other actinides and lanthanides. Old symbols for: 18 argon Ar (here: A), 43 technetium Tc (Ma, masurium, 1925, dismissed as an error and finally confirmed in 1937, Palermo), 54 xenon Xe (X), 86 radon, Rn (Em, emanation)

German chemists Walter Noddack, Otto Berg, and Ida Tacke reported the discovery of element 75 and element 43 in 1925, and named element 43 masurium (after Masuria in eastern Prussia, now in Poland, the region where Walter Noddack's family originated).[8] The group bombarded columbite with a beam of electrons and deduced element 43 was present by examining X-ray emission spectrograms.[9] The wavelength of the X-rays produced is related to the atomic number by a formula derived by Henry Moseley in 1913. The team claimed to detect a faint X-ray signal at a wavelength produced by element 43. Later experimenters could not replicate the discovery, and it was dismissed as an error for many years.[10][11] Still, in 1933, a series of articles on the discovery of elements quoted the name masurium for element 43.[12][note 1] Whether the 1925 team actually did discover element 43 is still debated.[13]

Official discovery and later history

The discovery of element 43 was finally confirmed in a 1937 experiment at the University of Palermo in Sicily by Carlo Perrier and Emilio Segrè.[14] In mid-1936, Segrè visited the United States, first Columbia University in New York and then the Lawrence Berkeley National Laboratory in California. He persuaded cyclotron inventor Ernest Lawrence to let him take back some discarded cyclotron parts that had become radioactive. Lawrence mailed him a molybdenum foil that had been part of the deflector in the cyclotron.[15]

Segrè enlisted his colleague Perrier to attempt to prove, through comparative chemistry, that the molybdenum activity was indeed from an element with the atomic number 43. In 1937, they succeeded in isolating the isotopes technetium-95m and technetium-97.[16][17] University of Palermo officials wanted them to name their discovery "panormium", after the Latin name for Palermo, Panormus. In 1947[16] element 43 was named after the Greek word τεχνητός, meaning "artificial", since it was the first element to be artificially produced.[6][8] Segrè returned to Berkeley and met Glenn T. Seaborg. They isolated the metastable isotope technetium-99m, which is now used in some ten million medical diagnostic procedures annually.[18]

In 1952, astronomer Paul W. Merrill in California detected the spectral signature of technetium (specifically wavelengths of 403.1 nm, 423.8 nm, 426.2 nm, and 429.7 nm) in light from S-type red giants.[19] The stars were near the end of their lives, yet were rich in this short-lived element, indicating that it was being produced in the stars by nuclear reactions. This evidence bolstered the hypothesis that heavier elements are the product of nucleosynthesis in stars.[17] More recently, such observations provided evidence that elements are formed by neutron capture in the s-process.[20]

Since that discovery, there have been many searches in terrestrial materials for natural sources of technetium. In 1962, technetium-99 was isolated and identified in pitchblende from the Belgian Congo in extremely small quantities (about 0.2 ng/kg);[20] there it originates as a spontaneous fission product of uranium-238. The Oklo natural nuclear fission reactor contains evidence that significant amounts of technetium-99 were produced and have since decayed into ruthenium-99.[20]