Orbitals Quotes (2 quotes)
The energy of a covalent bond is largely the energy of resonance of two electrons between two atoms. The examination of the form of the resonance integral shows that the resonance energy increases in magnitude with increase in the overlapping of the two atomic orbitals involved in the formation of the bond, the word ‘overlapping” signifying the extent to which regions in space in which the two orbital wave functions have large values coincide... Consequently it is expected that of two orbitals in an atom the one which can overlap more with an orbital of another atom will form the stronger bond with that atom, and, moreover, the bond formed by a given orbital will tend to lie in that direction in which the orbital is concentrated.
Nature of the Chemical Bond and the Structure of Molecules and Crystals (1939), 76.
Theoretical chemistry is a peculiar subject. It is based on an equation that can hardly ever be solved.
'Orbital Update', review of R. McWenny, Methods of Molecular Quantum Mechanics (1989). Nature, 1990, 343, 222.