Germanium – facts and properties
- Symbol
- Ge
- Atomic number
- 32
- Atomic mass
- 72.63 u
- Period
- 4
- Group
- 14
- Category
- metalloid
- Electron configuration
- [Ar] 3d¹⁰ 4s² 4p²
- Electronegativity
- 2.01
- Atomic radius
- 125 pm
- Valence electrons
- 4
- State at standard conditions
- solid
- Melting point
- 938.3 °C
- Boiling point
- 2833 °C
- Density
- 5.323 g/cm³
- Discovered
- 1886
Germanium is a shiny, hard and brittle metalloid with atomic number 32. It looks like a grey-white metal but behaves like a semiconductor. The first transistor was built with germanium, and the element is still found in fibre-optic cables and in lenses for thermal cameras. Mendeleev predicted it years before its discovery and called it eka-silicon. It was found in Germany, and its name recalls that.
Position in the periodic table
Occurrence and extraction
Germanium is rare and forms hardly any deposits of its own. The mineral argyrodite, a silver germanium sulfide, is a notable exception and was found in 1885 in a mine near Freiberg in Saxony. Industrially, though, traces in other raw materials matter more: zinc ores such as zinc blende contain a little germanium, and it also concentrates in the fly ash of some coal-fired power stations. Germanium is therefore made almost entirely as a by-product of zinc production and coal processing. China is by far the largest producer, and the European Union also lists germanium as a critical raw material.
The chemist Clemens Winkler at the mining academy in Freiberg examined argyrodite and noticed that his analysis came up short by a few percent. He concluded that a new element was present and isolated it in 1886. He named it after his homeland, Germania. In 1871 Mendeleev had predicted an element with the atomic mass and compounds that suit germanium and called it eka-silicon. Winkler's measurements confirmed the prediction.
Electronics needs extremely pure germanium. First germanium dioxide is made, then reduced with hydrogen to the metal, and then purified by zone refining: a rod is melted section by section and the impurities travel with the molten zone to one end.
Properties and reactions
Germanium is in period 4 and group 14, directly below silicon. Its electron configuration is [Ar] 3d¹⁰ 4s² 4p², with 4 valence electrons. Its electronegativity is 2.01. The metalloid has a density of 5.323 g/cm³, melts at 938.3 °C and boils at 2833 °C. As in diamond, each atom is bonded tetrahedrally to four neighbours. The material is therefore hard but brittle and shatters when struck.
Germanium conducts electricity better than an insulator but worse than a metal. Unlike metals, its conductivity rises with temperature, because more electrons are lifted from the valence band into the conduction band. The energy needed for this, the band gap, is smaller in germanium than in silicon, so even at room temperature it has more free charge carriers than silicon, and near-infrared light can excite electrons. Deliberate impurities, called doping, control conductivity: arsenic supplies extra electrons, gallium creates holes.
Chemically germanium is fairly inert. It does not dissolve in hydrochloric acid and is attacked only by strong oxidising acids such as hot concentrated sulfuric or nitric acid. A thin oxide layer forms in air, but germanium dioxide is slightly soluble in water and less stable than silicon dioxide, one reason why silicon later displaced germanium in most chips. In compounds germanium is mostly tetravalent, though germanium(II) also exists.
Uses in everyday life and technology
The first transistor was made in 1947 at Bell Laboratories in the United States, and its semiconductor was germanium. John Bardeen, Walter Brattain and William Shockley received the Nobel Prize in Physics for it in 1956. Then silicon took over, because it is cheaper, tolerates higher temperatures and forms a stable oxide. Germanium has not vanished from chips, however: silicon-germanium layers raise the speed of some processors and high-frequency circuits.
Optics is a major use. Germanium is transparent to infrared radiation but opaque to visible light. Lenses and windows made of germanium are therefore found in thermal imaging cameras, night-vision devices and sensors that detect body heat. In optical fibres, germanium dioxide in the core raises the refractive index so that light is guided along the core. Solar cells for satellites are often built on germanium wafers, and very pure germanium crystals serve as detectors for gamma radiation.
Germanium has no proven function in the human body. Inorganic germanium compounds and organic preparations sold as food supplements have in some cases caused serious kidney damage.
Molecules containing this element
- Magnesium hexafluorogermanate MgGeF6
Quick question
What is the atomic number of germanium (Ge)?
FAQ
Why was the first transistor made of germanium?
By the late 1940s germanium could already be produced in purified form, and it is a semiconductor whose conductivity can be controlled by doping. The researchers at Bell Laboratories used that. Silicon later prevailed because it is cheaper and tolerates higher operating temperatures.
What is germanium used for today?
Mainly for infrared optics in thermal cameras, for the core of optical fibres, for satellite solar cells and for silicon-germanium chips. Very pure germanium crystals also serve as detectors for gamma radiation.
What was eka-silicon?
This was Mendeleev's name in 1871 for an element he expected below silicon. He predicted its atomic mass and the formulas of its compounds, among other things. When Clemens Winkler discovered germanium in 1886, the values matched so well that the periodic table convinced the sceptics as an ordering principle.