Covalent Bonds, Lewis Formulas, and the Octet Rule

3 Covalent Bonds, Lewis Formulas, and the Octet Rule 

The covalent, or shared electron pair, model of chemical bonding was first suggested by G. N. Lewis of the University of California in 1916. Lewis proposed that a sharing of two electrons by two hydrogen atoms permits each one to have a stable closed-shell electron configuration analogous to helium. 

Two hydrogen atoms, each with a single electron 

Hydrogen molecule covalent bonding by way of a shared electron pair 

The amount of energy required to dissociate a hydrogen molecule H2 to two separate hydrogen atoms is its bond dissociation enthalpy. For H2 it is quite large, amounting to -1-435 kJ/mol (-1-104 kcal/mol). The main contributor to the strength of the covalent bond in H2 is the increased Coulombic force exerted on its two electrons. Each electron in H2 feels the attractive force of two nuclei, rather than one as it would in an isolated hydrogen atom. 

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