Germanium

Germanium is a metalloid in group 14, between silicon and tin, with four valence electrons ([Ar]3d10 4s2 4p2). Like silicon, each atom forms four covalent bonds in a diamond-like crystal, making it a brittle, lustrous gray-white solid. Its band gap, the energy needed to free an electron for conduction, is only 0.67 electronvolts, compared with 1.12 for silicon. That makes germanium an easier semiconductor to work with, but also more sensitive to heat. Its compounds are mainly in the +4 state, such as germanium dioxide and germanium tetrachloride.

The first transistor, built at Bell Labs in 1947, used germanium, and germanium dominated early electronics until silicon took over in the 1960s, because silicon works at higher temperatures and forms a stable insulating oxide. Today germanium has found new roles. Germanium dioxide raises the refractive index of the glass core in optical fibers. Germanium crystals are transparent to infrared light, so they serve as lenses in thermal cameras, and germanium wafers carry the multi-junction solar cells that power spacecraft.

Discovery

In 1871 Mendeleev predicted eka-silicon, a missing element below silicon with an atomic mass of about 72 and a density of about 5.5 g/cm3. In 1886 Clemens Winkler, analyzing the silver mineral argyrodite from Freiberg in Saxony, found an unexplained shortfall of about 7 percent in his results and tracked it down to a new element. Its properties closely matched the prediction. Winkler named it after his country, Germany (Latin Germania).