Electron pairbond

The leading term represents a structure with an electron pairbond between one H and the 5a orbital and another between the other H and the 2n y orbital. 

The two MO approaches to polyatomic systems, localized and delocalized, are useful in different circumstances. When localized descriptions are possible, they correspond more closely to the simple chemical pictures of electron-pairbonds provided by the Lewis and VSEPR models. Such descriptions are not always possible, and 3c or other delocalized models provide an alternative to the resonance approach (see below and Topic Cl). Delocalized MO theory is also more useful for interpreting electronic spectra of molecules. 

The idea of the covalent bond was first suggested by the American physical chemist Gilbert Newton Lewis (1875-1946) in 1916. He pointed out that the electron configuration of the noble gases appears to be a particularly stable one. Noble-gas atoms are themselves extremely unreactive. Moreover, as pointed out in Chapter 6, a great many monatomic ions have noble-gas structures. Lewis suggested that nonmetal atoms, by sharing electrons to form an electron-pairbond, can acquire a stable noble-gas structure. Consider,... 

A fourth type of flee radical reaction, in which one reactant molecnle has an impaired electron that occnpies an atomic orbital, and the other species has an electron-pairbond, is customarily represented as (d). 

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