Hydrogen bond
Hydrogen bonds can vary in strength from weak (1–2 kJ mol) to strong (161.5 kJ mol in the ion ). Typical enthalpies in vapor include:
Bond cleavage
The singlet excitation energy of a sigma bond is the energy required for heterolytic dissociation, but the actual singlet excitation energy may be lower than the bond dissociation energy of heterolysis as a result of the Coulombic attraction between the two ion fragments. The singlet excitation energy of a silicon–silicon sigma bond is lower than the carbon–carbon sigma bond, even though their bond strengths are 80kJ/mol and 70kJ/mol respectively, because silicon has higher electron affinity and lower ionization potential than carbon.