and the other second-shell nonmetals, except fluorine, have another
very special property: they can share more than one electron pair
with the same neighbor atom, thereby creating double and triple bonds.
Ethane (right) is a two-carbon compound with only single electron-pair
is a two-carbon compound with a double bond between the carbon atoms
(right). Each carbon atom still shares four electron pairs, but with
only three neighbors in ethylene instead of four as in ethane. In
acetylene, H-CC-H, the carbon atoms are bound together by three electron
pairs in a triple bond (right). For reasons that will become apparent
in Chapter 9, two carbon atoms cannot share four electron pairs in
a quadruple bond.