This book provides a systematic description of the molecular structures and bonding in simple compounds of the main group elements with particular emphasis on bond distances, bond energies and coordination geometries. The description includes the structures of hydrogen, halogen and methyl derivatives of the elements in each group, some of these molecules are ionic, some polar covalent. The survey of molecules whose structures conform to well-established trends isfollowed by representative examples of molecules that do not conform. We also describe electron donor-acceptor and hydrogen bonded complexes. Chemists use models to systematize our knowledge, to memorize information and to predict the structures of compounds that have not yet been studied. The book provides a lucid discussion of a number of models such as the Lewis electron-pair bond and the VSEPR models, the spherical and polarizable ion models, and molecular orbital calculations, and it outlines the successes and failures of each.