A single covalent bond is build when two atoms share a pair of electrons. Triple and double bonds can be formed when two or three such pairs are shared. A Lewis structure is a representation of a complex ion or molecule that shows the disposition of valence electrons (inner shells are not drawn) around each atom. 1-4 show Lewis structures of CH4, O2, H2O and N2, the last two molecules having a double and triple bond, respectively. These representations are entirely equivalent to the valence structures (1′-4′) in which each bonding pair of electrons are represented by a line.