CARBON, SILICON AND GERMANIUM
With the valence electron configuration s2p2 the nonmetallic group of elements 14 may form compounds with four tetrahedrally directed covalent bonds. Only carbon forms strong and rigid multiple bonds and its compounds define many differences in properties and structure from those of Si and Ge. The metallic elements of the group (Pb and Sn), germanium has some stable and reliable divalent compounds.
The abundances of the elements by weight in the crust are: Si 27% (second only to oxygen), C and Ge Carbon is locating as carbonate minerals and in smaller amounts as the element and in hydrocarbon deposits. It is required in the atmosphere (as the greenhouse gas CO2) and is the major element of nature. Silicate minerals are the dominant chemical compounds of the underlying mantle and of the crust. Germanium is strongly but thinly distributed in silicate and sulfide minerals.