Mulliken electronegativity values

This was justified as follows. The energy required to take an electron from a neutral atom Y to a neutral atom Z is /Y — AZt whereas the energy cost to take an electron from a neutral atom Z to a neutral atom Y is Iz — Ay. Hence, the two atoms Y and Z would have an equal propensity for attracting electrons or equal electronegativity if /Y — Az = Iz — AY, that is if IY + Ay = Iz + Az. This is consistent with the Mulliken definition, eqn (3.35), the factor 1/2 being arbitrary. As can be seen by comparing the two different scales in Fig. 3.5, the Mulliken values are approximately 2.8 times the Pauling values. 

In one of the simplest approaches to electronegativity, Mulliken took the value of y for an atom to be the mean... 

FIGURE 3.2 The electronegativities of the elements in group lA calculated by Pauling, Mulliken, and Allred-Rochow methods (Mulliken values are not determined for Cs and Fr). 

In one of the simplest approaches to electronegativity, Mulliken took the value of x for an atom to be the mean of the values of the first ionization energy, IE, and the first electron affinity, EA (eq. 2.13). 

Nevertheless, Murrell, Kettle, and Tedder conclude in their book on valence theory57 that there is no correlation between the electric dipole moment of a bond and the electronegativity difference. They have plotted the values of the electric dipole moments of eight bonds against the difference in the values of the Mulliken electronegativity (see Figure 1-2). (The bond moments for OH, NH, PH, NF, and PF are calculated from the... 

Table 1-1 gives the values of the Mulliken electronegativity, the results of dividing these values by 2.69, and the values from The Nature of the Chemical Bond. (The factor 2.69 is the ratio of the sum of the first-row values to the sum of the third-row values.) The second reason for the failure to obtain a correlation is neglect of some of the structural features. Let us consider the factor 2.69 now. 

The negative n value means that the alkane carbon net charges are positive. This relatively important C -H polarity is in line with the view that hydrogen is certainly more electronegative than carbon, as Mulliken and Roothaan [110] and others [111-113] have pointed out. 

Other sets of electronegativities of the elements have been proposed. The rather direct, but somewhat limited, method of Mulliken makes use of the ionization potential IP and electron-affinity data (Table 3.3). Numerical values are obtained that coincide with values from other methods if electronegativities are calculated from... 

The Mulliken electronegativities have a good linear relationship with the Pauling values, and the former are usually adjusted for consistency... 

Like the Mulliken method, the Allred-Rochow method defines electronegativities in terms of atomic rather than molecular properties. Another objection is that it fails in the case of hydrogen the above equation yields a value which would give H an electronegativity comparable with O. The value of 2.2 for hydrogen is rather arbitrarily chosen. Nevertheless, the Allred-Rochow scale has won widespread acceptance among inorganic chemists who find it consistent with many features of chemical periodicity. 

For example, fluorine has the Pauling electronegativity of 4.0 and a value of 3.91 on the Mulliken scale. A different approach was used by Allred and Rochow to establish an electronegativity scale. This scale is based on a consideration of the electrostatic force holding a valence shell electron in an atom of radius, r, by an effective nuclear charge,... 

Table 7 indicates the good agreement between these values and values of Mulliken s electronegativity, given according to equation (151) by... 

---