The relative strengths of ionic, covalent and multiple-bonding in diatomic molecules

Abstract Values of the ratio [ D 0 : e 2 / r e ] are examined for diatomic molecules in which the bonding is essentially ionic, covalent, or multiple in character ( D 0 is the dissociation energy, and e 2 / r e the coulombic energy of attraction of point-changes at the internuclear bondlength, r e ). The ratio values in single-bonded diatomic molecules range from (0.75±0.17) in the essentially ionic alkali-metal halides, to (0.16±0.03) in the covalent alkali-metal dimers. For multiple-bonded covalent M 2 molecules, the ratio reaches 0.74 in triple-bonded N 2 and 0.56 in sextuple-bonded Mo 2 ; but in many first-row transition dimetals, multiple bonding does not lead to high ratio values. Higher ratios do occur in MO molecules. In relative terms, ionic character-in particular when associated with multiple bonding-is more effective than multiplicity per se in bond-strengthening.