◾ Roles of Silicon in Life on Earth and Elsewhere
Carbon is the ideal atom for the formation of varieties of stable, complex substances for several reasons. Because of its electronic structure and placement in the periodic table, carbon has a valence of four and hence can form four dierent bonds. Similarly, nitrogen can form only three bonds in its neutral forms, and oxygen only two. In a numbers game, two carbons singly bonded to each other still have six opportunities for further bonds, whereas two nitrogens have four and two oxygens only two. Carbon thus has an advantage in terms of variety and complexity.