Germanium

32 gallium ← germanium → arsenic Si ↑ Ge ↓ Sn periodic table
General
Name, Symbol, Number	germanium, Ge, 32
Chemical series	metalloids
Group, Period, Block	14, 4, p
Appearance	grayish white
Atomic mass	72.64(1) g/mol
Electron configuration	[Ar] 3d10 4s2 4p2
Electrons per shell	2, 8, 18, 4
Physical properties
Phase	solid
Density (near r.t.)	5.323 g/cm³
Liquid density at m.p.	5.60 g/cm³
Melting point	1211.40 K (938.25 °C, 1720.85 °F)
Boiling point	3106 K (2833 °C, 5131 °F)
Heat of fusion	36.94 kJ/mol
Heat of vaporization	334 kJ/mol
Heat capacity	(25 °C) 23.222 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1644 1814 2023 2287 2633 3104
Atomic properties
Crystal structure	Face-centered cubic
Oxidation states	4 (amphoteric oxide)
Electronegativity	2.01 (Pauling scale)
Ionization energies (more)	1st: 762 kJ/mol
	2nd: 1537.5 kJ/mol
	3rd: 3302.1 kJ/mol
Atomic radius	125 pm
Atomic radius (calc.)	125 pm
Covalent radius	122 pm
Miscellaneous
Magnetic ordering	no data
Thermal conductivity	(300 K) 60.2 W/(m·K)
Thermal expansion	(25 °C) 6.0 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 5400 m/s
Mohs hardness	6.0
CAS registry number	7440-56-4
Notable isotopes
Main article: Isotopes of germanium iso NA half-life DM DE (MeV) DP 68Ge syn 270.8 d ε - 68Ga 70Ge 21.23% Ge is stable with 38 neutrons 71Ge syn 11.26 d ε - 71Ga 72Ge 27.66% Ge is stable with 40 neutrons 73Ge 7.73% Ge is stable with 41 neutrons 74Ge 35.94% Ge is stable with 42 neutrons 76Ge 7.44% Ge is stable with 44 neutrons

Germanium (chemical symbol Ge, atomic number 32) is a lustrous, hard, grayish-white chemical element. It is classified as a metalloid—that is, its chemical properties are intermediate between those of metals and nonmetals. It is a valuable semiconductor material.

The development of the germanium transistor opened the door to numerous applications in solid-state electronics. Currently, germanium and its compounds are mainly used for fiber-optic communications networks and infrared night vision systems. In addition, germanium is a catalyst for certain polymerization reactions, and single-crystal detectors made with highly purified germanium can be used to identify sources of radiation. Germanium dioxide is useful for wide-angle camera lenses and microscope objective lenses, and silicon germanide is becoming an important semiconductor for high-speed integrated circuits.

Occurrence and extraction

Germanium (Latin Germania, for Germany) is found in argyrodite (sulfide of germanium and silver), coal, germanite, zinc ores, and other minerals.

Germanium is obtained commercially from the smelter dust of zinc ore processing and the combustion byproducts of certain coals. A large reserve of this element is found in coal sources.

This metalloid can be extracted from associated metals by fractional distillation of its volatile tetrachloride. This technique permits the production of ultra-high-purity germanium.

History

Dmitri Mendeleev predicted the existence of germanium (as well as other unidentified elements) in 1871. Thinking of it as a missing member of the silicon group, he called it ekasilicon. When the element was discovered by Clemens Winkler in 1886, it served as an important confirmation of Mendeleev's idea of element periodicity.

Property	Ekasilicon	Germanium
atomic mass	72	72.59
density	5.5	5.35
melting point (°C)	high	947
color	gray	gray

The development of the germanium transistor opened the door to countless applications in solid state electronics. 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. Silicon has superior electrical properties but requires much higher purity samples—a purity that could not be commercially achieved in the early days. Meanwhile, the demand for germanium increased dramatically for other applications—fiber optics communication networks, infrared night vision systems, and polymerization catalysts.

Notable characteristics

In the periodic table, germanium is located in group 14 (former group 4A), between silicon and tin, and in period 4, between gallium and arsenic. Like silicon and arsenic, it is a metalloid.

In its pure state, germanium is crystalline and brittle, and it retains its luster in air at room temperature. In terms of its atomic arrangement, it has the same crystal structure as diamond.

Germanium is a semiconductor, with electrical properties between those of a metal and an insulator. Unlike most semiconductors, it has a narrow band gap, allowing it to respond efficiently to infrared light. Zone refining techniques have enabled the production of extremely pure, crystalline germanium for semiconductors (with an impurity level of only one part in 10¹⁰).

Isotopes

The isotopes of germanium range in atomic mass number from 58 to 89. Of these, there are four stable isotopes: ⁷⁰Ge, ⁷²Ge, ⁷³Ge, and ⁷⁴Ge. In addition, ⁷⁶Ge has been found to have an extremely long half-life, so that for all practical purposes it may be considered stable. The other radioisotopes are very short-lived.

Compounds

• Germane (or germanium tetrahydride, GeH₄): It is the simplest germanium hydride and one of the most useful compounds of germanium. It is a gas at ordinary temperatures and pressures. Its molecules have a tetrahedral shape, similar to the molecules of silane (SiH₄) and methane (CH₄). It is flammable and, when burned in air, produces germanium dioxide (GeO₂) and water. The gas decomposes at a temperature of about 600K, yielding germanium and hydrogen. For this reason, the semiconductor industry uses germane as a starting material for growing germanium crystals, using an approach called epitaxy (the growth of a crystal on a crystalline substrate).^[1]

• Germanium dioxide (or germanium oxide or germania, GeO₂): This compound may come in the form of a white powder or colorless crystals, with a melting point of 1,115 °C. It is a structural analog of silicon dioxide (silica). It forms a “passivation layer” (protective surface film) on pure germanium that is in contact with atmospheric oxygen. The high refractive index and low optical dispersion of this oxide make it useful for wide-angle camera lenses and optical microscope lenses. A mixture of silicon dioxide and germanium dioxide ("silica-germania") is used for optical fibers and optical waveguides. As GeO₂ is transparent in the infrared region, it is useful for manufacturing infrared windows and lenses, for night-vision technology in the military and luxury vehicles.^[2]

• Germanium tetrachloride (GeCl₄): This colorless liquid is used as an intermediate in the production of purified germanium metal. In recent years, it is being used almost exclusively as an intermediate for the production of GeO₂, an oxide glass with several unique properties and applications, noted above.

• Organogermanium compounds: These are organic compounds in which germanium atoms are directly bound to carbon atoms.^[3]. Examples are tetramethyl germanium and tetraethyl germanium. The chemistry of these compounds lies between that of organosilicon and organotin compounds. Organogermanium compounds are advocated as nontoxic alternatives to many toxic organotin reagents. Compounds such as tetramethyl germanium and tetraethyl germanium are used in the microelectronics industry as precursors for germanium oxide chemical vapor deposition processes.

Applications

• As germanium responds efficiently to infrared light, it is useful for infrared spectroscopes and other optical equipment requiring highly sensitive infrared detectors.

• The index of refraction and dispersion properties of germanium oxide make it useful in wide-angle camera lenses and microscope objective lenses.

• Silicon germanide (or "silicon-germanium," SiGe) is rapidly becoming an important semiconductor material for use in high-speed integrated circuits.

• Germanium may be used as a phosphor in fluorescent lamps.

• It is a catalyst for certain polymerization reactions.

• Single-crystal detectors made with high-purity germanium can precisely identify sources of radiation. These devices can be useful for airport security.

• Some compounds of germanium are useful as chemotherapeutic agents, because they are toxic for certain bacteria but have low toxicity toward mammals.

• Vintage acoustic stompboxes containing germanium transistors have markedly increased in collector value for their distinctive tonal quality.

• In recent years, germanium is being increasingly used in precious metal alloys. For instance, in sterling silver (an alloy of silver with copper or other metals), the presence of germanium has been found to increase tarnish resistance and reduce firescale (a red or purple stain that appears).

Precaution

Germanium has been called an attractive nutritional supplement, able to cure diseases such as cancer and AIDS. As noted above, some germanium compounds are toxic for bacteria but have low toxicity toward mammals. Yet, a 1997 study sponsored by the U.S. Food and Drug Administration concluded that nutritional supplements containing germanium "present potential human health hazard."^[4]

See also

• Chemical element
• Metalloid
• Periodic table

Notes

References

ISBN links support NWE through referral fees

• Hammond, C. R. "The Elements" in David R. Lide (ed.), CRC Handbook of Chemistry and Physics, 85th ed. Boca Raton, FL: CRC Press, 2004. ISBN 0849304857
• Yamamoto, Hisashi and Koichiro Oshima (eds.). Main Group Metals in Organic Synthesis. Hoboken, NJ: John Wiley & Sons, 2004. ISBN 3527305084

External links

All links retrieved June 20 2017.

• WebElements.com – Germanium