Salient Features of VB Theory

VB theory's key working rules, drawn out from the H₂ picture above and generalised to any covalent bond:

1. A covalent bond forms when a HALF-FILLED orbital of one atom overlaps with a half-filled orbital of another atom.
2. The resulting overlapped orbital is occupied by TWO electrons of OPPOSITE spin (e.g. in H₂, the two 1s electrons, one from each hydrogen, pair up and occupy the overlap region together).
3. The STRENGTH of a covalent bond depends on the EXTENT of orbital overlap -- the greater the overlap, the larger the energy released on bond formation, and the stronger the resulting bond. …