Germanium

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Germanium,  32Ge
General properties
Name, symbol Germanium, Ge
Allotropes α-Ge, β-Ge
Appearance Lustrous gray
Germanium in the periodic table
Si

Ge

Sn
GalliumGermaniumArsenic
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)
· references

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 alkalis, but reacts slowly with concentrated sulfuric acid and violently with molten alkalis to produce germanates ([GeO3]2−).

Germanium halides hydrolyze in water or moist air.

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 carbide.

Projects

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