Germanium

Germanium,  ₃₂Ge

General properties
Name, symbol	Germanium, Ge
Allotropes	α-Ge, β-Ge
Appearance	Lustrous gray
Germanium in the periodic table
Si ↑ Ge ↓ Sn Gallium ← Germanium → Arsenic
Atomic number	32
Standard atomic weight (Ar)	72.630(8)
Group, block	(carbon group); p-block
Period	period 4
Electron configuration	[Ar] 3d10 4s2 4p2
per shell	2, 8, 18, 4
Physical properties
Lustrous gray
Phase	Solid
Melting point	1211.40 K ​(938.25 °C, ​​1720.85 °F)
Boiling point	3106 K ​(2833 °C, ​​5131 °F)
Density near r.t.	5.323 g/cm3
when liquid, at	5.60 g/cm3
Heat of fusion	36.94 kJ/mol
Heat of	334 kJ/mol
Molar heat capacity	23.222 J/(mol·K)
pressure
Atomic properties
Oxidation states	4, 3, 2, 1, 0, −1, −2, −3, −4 ​(an amphoteric oxide)
Electronegativity	Pauling scale: 2.01
energies	1st: 762 kJ/mol 2nd: 1537.5 kJ/mol 3rd: 3302.1 kJ/mol
Atomic radius	empirical: 122 pm
Covalent radius	122 pm
Van der Waals radius	211 pm
Miscellanea
Crystal structure	​Face-centered diamond-cubic
Speed of sound thin rod	5400 m/s (at 20 °C)
Thermal expansion	6.0 µm/(m·K)
Thermal conductivity	60.2 W/(m·K)
Electrical resistivity	1 Ω·m (at 20 °C)
Young's modulus	103 GPa
Shear modulus	41 GPa
Bulk modulus	75 GPa
Poisson ratio	0.26
Mohs hardness	6.0
CAS Registry Number	7440-56-4
History
Naming	After Germany, homeland of the discoverer
Prediction	Dmitri Mendeleev (1871)
Discovery	Clemens Winkler (1886)

Germanium is a chemical element with symbol Ge and atomic number 32. It is a metalloid.

Properties

Chemical

Elemental germanium is stable in air, and slowly oxidizes to GeO₂ at 250 °C. Germanium is insoluble in dilute acids and alkali, but reacts slowly with concentrated sulfuric acid and violently with molten alkali to produce germanates ([GeO₃]²⁻).

Germanium halides hydrolyze in water or moist air, to yield hydrogen halides and germanium oxide.

Physical

Germanium is a brittle, silvery-white, semi-metallic element. It posses two allotrope forms:

• α-germanium: the form at standard conditions. It has a metallic luster and a diamond cubic crystal structure.
• β-germanium: forms at pressures above 120 kbar. It posses the same structure as β-tin.

Extremely pure germanium will spontaneously extrude very long screw dislocations. This is the primary reason why old transistors fail.

Along with antimony, bismuth, gallium, silicon and water, it is one of the few substances that expands as it solidifies. Germanium is a semiconductor.

Availability

Germanium can be found in very old transistors and diodes, albeit the amount is small.

Pure germanium can be purchased from Metallium, at $11/g. It is very easy to find extremely pure germanium, as it is used in certain semiconductors.

Preparation

Elemental germanium can be prepared by reducing germanium dioxide (germania) with hydrogen.

GeO₂ + H₂ → Ge + H₂O

This reaction requires high temperatures.

Germanium is less reactive than silicon, so carbon can also be used as a reducing agent.

GeO₂ + C → Ge + CO₂

Unlike in the case of silicon, this reduction will yield only a small quantity of germanium carbide.

Projects

• Make germanium dioxide
• Make germane (GeH₄)

Handling

Safety

Pure germanium has low toxicity, however its compounds have different biological effects. Inorganic germanium compounds tend to accumulate inside the body and will cause health related problems. Organic germanium compounds have been shown to be less toxic and some even have beneficial properties.

Storage

Germanium reacts very slowly in air to produce a thin protective layer of germania. No special storage is required.

Disposal

Germanium is present only in traces in nature. Germania is inert so it does not pose environmental hazard, and may be dumped in the trash. Inorganic germanium compounds should be converted to germania before discarding or recycling.

References

Relevant Sciencemadness threads

• Dissolving germanium metal