Electronegativity, metals Mulliken scale

There is a linear correlation between the empirical electronegativity (Pauling scale) and hardness and the absolute electronegativity (Mulliken electronegativity) for the nontransition metals ... 

However, we cannot exclude the s-basis set electronegativity scale just through comparison between scales since other similar discrepancies appear (even in the main groups) when the Mulliken-Jaffe and the Xa methods are compared, for instance (see the Table 4.12). In any case, the present s-basis set results may help in judging also the various criteria of validity for an electronegativity scale, see Section 4.7.2. Looking to the transition metal... 

The (X is electronegativity and r is ionic radius) reflects the degree of covalent interactions in the metal-ligand complex relative to ionic interactions (Nieboer and Richardson 1980). In QSAR studies, the covalent index is commonly used in combination with ionic index T lr or with the constant for the first hydrolysis Hog KOHI (see Section 3.5). The subscript m refers to the most common (Mulliken) measure of electronegativity. Sometimes other measures are used in the literature and sometimes the m is omitted, e.g., the covalence index in Chapter 8 does not include the m subscript because the Pauling, Mulliken or Allred-Rochow scales for electronegativity might be pertinent. 

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