Carbon, with six protons in its nucleus, is the Don Juan of these atomic romances. It normally has four electrons in its outer orbit, but there is room enough there for eight, so you can make a carbon atom happy by removing four electrons from its outer shell, by adding four electrons, or by letting it share four electrons with another atom. This gives it a lot of options, and that is why carbon can form complicated molecules with rings, chains, and other exotic shapes. Its virtuosity explains why carbon is so important to the chemistry of life. The basic
