Germanium

Germanium, 32Ge
Grayish lustrous block with uneven cleaved surface
Germanium
Pronunciationm/ (MAY-nee-əm)
Appearancegrayish-white
Standard atomic weight Ar, std(Ge)72.630(8)[1]
Germanium in the periodic table
HydrogenHelium
LithiumBerylliumBoronCarbonNitrogenOxygenFluorineNeon
SodiumMagnesiumAluminiumSiliconPhosphorusSulfurChlorineArgon
PotassiumCalciumScandiumTitaniumVanadiumChromiumManganeseIronCobaltNickelCopperZincGalliumGermaniumArsenicSeleniumBromineKrypton
RubidiumStrontiumYttriumZirconiumNiobiumMolybdenumTechnetiumRutheniumRhodiumPalladiumSilverCadmiumIndiumTinAntimonyTelluriumIodineXenon
CaesiumBariumLanthanumCeriumPraseodymiumNeodymiumPromethiumSamariumEuropiumGadoliniumTerbiumDysprosiumHolmiumErbiumThuliumYtterbiumLutetiumHafniumTantalumTungstenRheniumOsmiumIridiumPlatinumGoldMercury (element)ThalliumLeadBismuthPoloniumAstatineRadon
FranciumRadiumActiniumThoriumProtactiniumUraniumNeptuniumPlutoniumAmericiumCuriumBerkeliumCaliforniumEinsteiniumFermiumMendeleviumNobeliumLawrenciumRutherfordiumDubniumSeaborgiumBohriumHassiumMeitneriumDarmstadtiumRoentgeniumCoperniciumNihoniumFleroviumMoscoviumLivermoriumTennessineOganesson
Si

Ge

Sn
galliumgermaniumarsenic
Atomic number (Z)32
Groupgroup 14 (carbon group)
Periodperiod 4
Blockp-block
Element category  Metalloid
Electron configuration[Ar] 3d10 4s2 4p2
Electrons per shell2, 8, 18, 4
Physical properties
Phase at STPsolid
Melting point1211.40 K ​(938.25 °C, ​1720.85 °F)
Boiling point3106 K ​(2833 °C, ​5131 °F)
Density (near r.t.)5.323 g/cm3
when liquid (at m.p.)5.60 g/cm3
Heat of fusion36.94 kJ/mol
Heat of vaporization334 kJ/mol
Molar heat capacity23.222 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)164418142023228726333104
Atomic properties
Oxidation states−4 −3, −2, −1, 0,[2] +1, +2, +3, +4 (an amphoteric oxide)
ElectronegativityPauling scale: 2.01
Ionization energies
  • 1st: 762 kJ/mol
  • 2nd: 1537.5 kJ/mol
  • 3rd: 3302.1 kJ/mol
Atomic radiusempirical: 122 pm
Covalent radius122 pm
Van der Waals radius211 pm
Color lines in a spectral range
Spectral lines of germanium
Other properties
Natural occurrenceprimordial
Crystal structureface-centered diamond-cubic
Diamond cubic crystal structure for germanium
Speed of sound thin rod5400 m/s (at 20 °C)
Thermal expansion6.0 µm/(m·K)
Thermal conductivity60.2 W/(m·K)
Electrical resistivity1 Ω·m (at 20 °C)
Band gap0.67 eV (at 300 K)
Magnetic orderingdiamagnetic[3]
Magnetic susceptibility−76.84·10−6 cm3/mol[4]
Young's modulus103 GPa[5]
Shear modulus41 GPa[5]
Bulk modulus75 GPa[5]
Poisson ratio0.26[5]
Mohs hardness6.0
CAS Number7440-56-4
History
Namingafter Germany, homeland of the discoverer
PredictionDmitri Mendeleev (1869)
DiscoveryClemens Winkler (1886)
Main isotopes of germanium
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct
68Gesyn270.95 dε68Ga
70Ge20.52%stable
71Gesyn11.3 dε71Ga
72Ge27.45%stable
73Ge7.76%stable
74Ge36.7%stable
76Ge7.75%1.78×1021 yββ76Se
| references

Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard-brittle, grayish-white metalloid in the carbon group, chemically similar to its group neighbours silicon and tin. Pure germanium is a semiconductor with an appearance similar to elemental silicon. Like silicon, germanium naturally reacts and forms complexes with oxygen in nature.

Because it seldom appears in high concentration, germanium was discovered comparatively late in the history of chemistry. Germanium ranks near fiftieth in relative abundance of the elements in the Earth's crust. In 1869, Dmitri Mendeleev predicted its existence and some of its properties from its position on his periodic table, and called the element ekasilicon. Nearly two decades later, in 1886, Clemens Winkler found the new element along with silver and sulfur, in a rare mineral called argyrodite. Although the new element somewhat resembled arsenic and antimony in appearance, the combining ratios in compounds agreed with Mendeleev's predictions for a relative of silicon. Winkler named the element after his country, Germany. Today, germanium is mined primarily from sphalerite (the primary ore of zinc), though germanium is also recovered commercially from silver, lead, and copper ores.

Elemental germanium is used as a semiconductor in transistors and various other electronic devices. Historically, the first decade of semiconductor electronics was based entirely on germanium. Presently, the major end uses are fibre-optic systems, infrared optics, solar cell applications, and light-emitting diodes (LEDs). Germanium compounds are also used for polymerization catalysts and have most recently found use in the production of nanowires. This element forms a large number of organogermanium compounds, such as tetraethylgermanium, useful in organometallic chemistry. Germanium is considered a technology-critical element.

Germanium is not thought to be an essential element for any living organism. Some complex organic germanium compounds are being investigated as possible pharmaceuticals, though none have yet proven successful. Similar to silicon and aluminium, natural germanium compounds tend to be insoluble in water and thus have little oral toxicity. However, synthetic soluble germanium salts are nephrotoxic, and synthetic chemically reactive germanium compounds with halogens and hydrogen are irritants and toxins.

History

Prediction of germanium, "?=70" (periodic table 1869)

In his report on The Periodic Law of the Chemical Elements in 1869, the Russian chemist Dmitri Mendeleev predicted the existence of several unknown chemical elements, including one that would fill a gap in the carbon family, located between silicon and tin.[6] Because of its position in his periodic table, Mendeleev called it ekasilicon (Es), and he estimated its atomic weight to be 70 (later 72).

In mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of its high silver content.[note 1] The chemist Clemens Winkler analyzed this new mineral, which proved to be a combination of silver, sulfur, and a new element. Winkler was able to isolate the new element in 1886 and found it similar to antimony. He initially considered the new element to be eka-antimony, but was soon convinced that it was instead eka-silicon.[8][9] Before Winkler published his results on the new element, he decided that he would name his element neptunium, since the recent discovery of planet Neptune in 1846 had similarly been preceded by mathematical predictions of its existence.[note 2] However, the name "neptunium" had already been given to another proposed chemical element (though not the element that today bears the name neptunium, which was discovered in 1940).[note 3] So instead, Winkler named the new element germanium (from the Latin word, Germania, for Germany) in honor of his homeland.[9] Argyrodite proved empirically to be Ag8GeS6. Because this new element showed some similarities with the elements arsenic and antimony, its proper place in the periodic table was under consideration, but its similarities with Dmitri Mendeleev's predicted element "ekasilicon" confirmed that place on the periodic table.[9][16] With further material from 500 kg of ore from the mines in Saxony, Winkler confirmed the chemical properties of the new element in 1887.[8][9][17] He also determined an atomic weight of 72.32 by analyzing pure germanium tetrachloride (GeCl
4
), while Lecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the spark spectrum of the element.[18]

Winkler was able to prepare several new compounds of germanium, including fluorides, chlorides, sulfides, dioxide, and tetraethylgermane (Ge(C2H5)4), the first organogermane.[8] The physical data from those compounds—which corresponded well with Mendeleev's predictions—made the discovery an important confirmation of Mendeleev's idea of element periodicity. Here is a comparison between the prediction and Winkler's data:[8]

Property Ekasilicon
Mendeleev
prediction (1871)
Germanium
Winkler
discovery (1887)
atomic mass 72.64 72.59
density (g/cm3) 5.5 5.35
melting point (°C) high 947
color gray gray
oxide type refractory dioxide refractory dioxide
oxide density (g/cm3) 4.7 4.7
oxide activity feebly basic feebly basic
chloride boiling point (°C) under 100 86 (GeCl4)
chloride density (g/cm3) 1.9 1.9

Until the late 1930s, germanium was thought to be a poorly conducting metal.[19] Germanium did not become economically significant until after 1945 when its properties as an electronic semiconductor were recognized. During World War II, small amounts of germanium were used in some special electronic devices, mostly diodes.[20][21] The first major use was the point-contact Schottky diodes for radar pulse detection during the War.[19] The first silicon-germanium alloys were obtained in 1955.[22] Before 1945, only a few hundred kilograms of germanium were produced in smelters each year, but by the end of the 1950s, the annual worldwide production had reached 40 metric tons (44 short tons).[23]

The development of the germanium transistor in 1948[24] opened the door to countless applications of solid state electronics.[25] From 1950 through the early 1970s, this area provided an increasing market for germanium, but then high-purity silicon began replacing germanium in transistors, diodes, and rectifiers.[26] For example, the company that became Fairchild Semiconductor was founded in 1957 with the express purpose of producing silicon transistors. Silicon has superior electrical properties, but it requires much greater purity that could not be commercially achieved in the early years of semiconductor electronics.[27]

Meanwhile, the demand for germanium for fiber optic communication networks, infrared night vision systems, and polymerization catalysts increased dramatically.[23] These end uses represented 85% of worldwide germanium consumption in 2000.[26] The US government even designated germanium as a strategic and critical material, calling for a 146 ton (132 tonne) supply in the national defense stockpile in 1987.[23]

Germanium differs from silicon in that the supply is limited by the availability of exploitable sources, while the supply of silicon is limited only by production capacity since silicon comes from ordinary sand and quartz. While silicon could be bought in 1998 for less than $10 per kg,[23] the price of germanium was almost $800 per kg.[23]