Germanium

Facts about germanium

Germanium is a chemical element or hard, lustrous, grayish white metalloid of group-14 of the periodic table with the symbol Ge and atomic number 32. It is used mainly for making optical parts in the infrared spectrometer.

The general trends in chemistry of group-14 or carbon group follow the typical pattern of the boron group. The trend of periodic table properties of group 14 elements is largely understood by their electronic configuration. The effect of shielding electrons of d and f orbitals is predominant for Ge and Pb.

The high melting point in carbon indicates high C-C bond energy with the diamond-type crystal lattice. Germanium also has a diamond-type crystal lattice but the larger size and weaker bond energy result in a lower melting point in Ge.

Where is germanium found?

It is not found widely in ores. Germanium is found with zinc and silver minerals. It is mined in Alaska, Tennessee, China, United Kingdom, Ukraine, Russia, and Belgium.

Isotopes of element

Germanium has five stable isotopes with mass numbers 70, 72, 73, 74, 76. Among these, ⁷⁶Ge is radioactive in nature with a half-life of 1.78 × 10²¹ years.

The relative abundance of these isotopes is given below the table,

Isotopes of germanium
Isotope	Abundance
70Ge	20.5%
72Ge	27.4%
73Ge	7.8%
74Ge	36.5%
76Ge	7.8%

Properties of germanium

It has a diamond-type crystal lattice. But the larger size and weak bond energy result in a lower melting point than silicon or carbon.  The electronegativity of Ge is slightly greater than that of silicon or tin.

The chemical reactivity and electrical conductance of group-14 elements increase down in the group.

• The energy gap between bonding and antibonding orbitals in carbon is very large. Therefore, it is an insulator.
• The energy gaps in Si, Ge, and Sn are 108, 64, and 7.7 kJ/mol respectively. Therefore, they are good semiconductors.

Elemental germanium burns slowly in the air to form GeO₂. It is insoluble in dilute acids or alkalies but dissolves in hot concentrated sulfuric acid or nitric acid.

Germanium
Symbol	Ge
Discovery	Discovered by Clemens Winkler in 1886
Name derived from	The Latin name of Germany, Germania
Common isotopes	32Ge73 and 32Ge74
Periodic properties
Atomic number	32
Atomic weight	72.63
Electron per shell	2, 8, 18, 4
Electronic configuration	[Ar] 3d10 4s2 4p2
Group	14
Period	4
Block	p-block
Physical properties
State at 20 °C	Solid
Melting point	938.25 °C
Boiling point	2833 °C
Density	5.323 g/cm3
Molar heat capacity	23.222 J mol−1 K−1
Electrical resistivity	1.00 nΩ m
Crystal structure	​face-centered diamond-cubic
Chemical properties
Atomic radius (non-bonded)	2.11 Å
Covalent radius	1.20 Å
Common oxidation number	+2, +4
Electronegativity	2.01 (Pauling scale)
Electron affinity	118.94 kJ mol−1
Ionization energy (kJ/mol)	1st	2nd	3rd
	762	1537.5	3302.1
CAS number	7440-56-4

Germanium in periodic table

Germanium is found in period 4 and group 14 or carbon family of periodic table.

It is a p-block element lies between silicon and tin in the periodic table.

Production process

Previously, Ge was recovered from coal ash. Now it is mostly obtained from the flue dust of zinc.

• The flue dust is leached with dilute sulfuric acid and the solution is slowly neutralized by the gradual addition of sodium hydroxide. At pH scale 2.4, GeO₂, xH₂O is precipitated which is 98 percent complete at pH 5.
• The mixed precipitate is heated with hydrochloric acid when volatile GeCl₄ is distilled out and ZnCl₂ is left behind. The GeCl₄ is purified by fractional distillation.
• GeCl₄ hydrolyzed to form GeO₂, xH₂O.
• GeO₂ is reduced to form Ge by hydrogen at 550 °C.
• Pure germanium is produced by zone refining.

Germanium compounds

Most of the compounds of group-14 elements are formed in +2 and +4 oxidation states. The high values of ionization energy suggest that the formation of M⁺⁴ ions would be rather unlikely except for Sn and Pb.

The compounds of germanium are mostly formed by covalent bonding. Some important chemical compounds of Ge are given below,

Tetrafluoride

The tetrahalides of germanium are readily prepared from the elements or by the action of HX on GeO₂. The physical properties of the tetrahalides are given below,

Compound	Nature	melting point (°C)	boiling point (°C)
GeF4	colourless gas	− 36.5	− 15
GeCl4	fuming liquid	− 49.5	86.5
GeI4	colourless liquid	26.1	186.5
GeBr4	red crystal	144	440

The tetrafluoride is prepared by the reaction of concentrated HF with GeO₂. It is a colorless hygroscopic gas with a boiling point of −36.5 °C.

Tetrachloride

Germanium tetrachloride is made by heating Ge in a stream of chlorine or by heating GeO₂ with fuming hydrochloric acid. It is a fuming liquid with a melting point of − 49.5 °C and a boiling point of 86.5 °C.

Germanium oxide

Germanium oxide is a white solid with the chemical formula GeO₂. It is sparingly soluble in water. GeO₂ is weakly acidic in nature, forming germinates with alkalies. It is forming GeCl₄ with concentrated HCl.

GeO₂ may be prepared by strongly heating the metalloid in oxygen or reacting of metalloid with concentrated nitric acid.

Uses of germanium

Modern developments in semiconductor technology began in the 1950s with the introduction of germanium transistors. The production of pure germanium is easier than that of pure silicon.

Methods to prepare ultrapure silicon were developed in the 1960s. Therefore, silicon transistors are now widely used due to their superior quality. Hence the use of germanium transistors is now declined.

• Presently, germanium is used for making optical parts of infrared spectrometers.
• The compound, Germania (GeO₂) is used for making wide-angle camera lenses, microscopy, and the core part of optical fibers due to its high refraction index and low optical dispersion.
• Germanium dioxide is also used as a chemical catalyst for the polymerization or production of polyethylene terephthalate.
• Silicon germanium alloys or semiconductors are used for making high-speed integrated circuits.