Durrant has proposed an alternative definition of hypervalency, based on the analysis of atomic charge maps obtained from atoms in molecules theory.  This approach defines a parameter called the valence electron equivalent, γ, as “the formal shared electron count at a given atom, obtained by any combination of valid ionic and covalent resonance forms that reproduces the observed charge distribution”.  For any particular atom X, if the value of γ(X) is greater than 8, that atom is hypervalent. Using this alternative definition, many species such as PCl, , and XeF, that are hypervalent by Musher's definition, are reclassified as hypercoordinate but not hypervalent, due to strongly ionic bonding that draws electrons away from the central atom.  On the other hand, some compounds that are normally written with ionic bonds in order to conform to the octet rule, such as ozone O, nitrous oxide NNO, and trimethylamine N-oxide , are found to be genuinely hypervalent. Examples of γ calculations for phosphate  (γ(P) = 2.6, non-hypervalent) and orthonitrate  (γ(N) = 8.5, hypervalent) are shown below.