Sunday, January 23, 2011

Carbon group

The carbon group is a periodic table group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and ununquadium (Uuq). In modern IUPAC notation, it is called Group 14. In the old IUPAC and CAS systems, it was called Group IVB and Group IVA, respectively.^[1] In the field of semiconductor physics, it is still universally called Group IV. The group was once also known as the tetrels (from Greek tetra, four), stemming from the Roman numeral IV in the group names, or (not coincidentally) from the fact that these elements have four valence electrons. Each of the elements in this group has 4 electrons in its outer energy level. The last orbital of all these elements is the p^2 orbital. In most cases, the elements share their electrons. The tendency to lose electrons increases as the size of the atom increases, as it does with increasing atomic number. Carbon alone forms negative ions, in the form of carbide (C^4−) ions. Silicon and germanium, both metalloids, each can form +4 ions. Tin and lead both are metals while ununquadium is a synthetic short-lived radioactive metal. Tin and lead are both capable of forming +2 ions.

Except for germanium and ununquadium, all of these elements are familiar in daily life either as the pure element or in the form of compounds. However, except for silicon, none of these elements are particularly plentiful in the Earth’s crust. Carbon forms a very large variety of compounds, in both the plant and animal kingdoms. Silicon and silicate minerals are fundamental components of the Earth’s crust; silica (silicon dioxide) is sand.

Tin and lead, although with very low abundances in the crust, are nevertheless common in everyday life. They occur in highly concentrated mineral deposits, can be obtained easily in the metallic state from those minerals, and are useful as metals and as alloys in many applications. Germanium, on the other hand, forms few characteristic minerals and is most commonly found only in small concentrations in association with the mineral zinc blende and in coals. Although germanium is indeed one of the rarer elements, it assumed importance upon recognition of its properties as a semiconductor.

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