Electronegativity equalization Pauling

Bratsch, S.G. Electronegativity Equalization with Pauling Units J. Chem. Educ. 1984, 61, 588-589. 

Bratsch SG (1984) Electronegativity equalization with Pauling units. J Chem Educat 61 588-... 

As has just been described, when a covalent bond forms between two atoms, there is no reason to assume that the pair of electrons is shared equally between the atoms. What is needed is some sort of way to provide a relative index of the ability of an atom to attract electrons. Linus Pauling developed an approach to this problem by describing a property now known as the electronegativity of an atom. This property gives a measure of the tendency of an atom in a molecule to attract electrons. Pauling devised a way to give numerical values to describe this property that makes use of the fact that the covalent bonds between atoms of different electronegativity are more stable than if they were purely... 

One classical example that apphes the electroneutrality principle is the electronic structure of carbon monoxide, a diatomic molecule with a very small dipole moment of 0.110 debye. The only electronic structure that satisfies the octet rule for CO is C=0 , a structure that corresponds to C and O, if the shared electron pairs are equally devided by the two atoms. Pauling showed that the electronegativity difference of 1.0 would correspond to about 22% partial ionic character for each bond, and to charges of and 0° +. A second possible electronic structure, C=O , does not complete the octet for carbon. The partial ionic character of the bonds corresponds to C0.44+ If these two structures contribute... 

Here/j is the fractional ionic character of the bond while Xf and X are the Pauling electronegativities of the elements A and B. It is seen that/- = 0 when = Xg and fi= I whenX — Vg 1. In crystals, this expression is modified to account for the fact that an atom forms more than one bond and the number of bonds formed is not always equal to its formal valence. For crystals, the expression for ionicity reads as... 

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. 

The energy of a partially ionic covalent bond between two atoms (A and B) is equal to the energy expected from a strictly covalent bond between the two atoms plus an amount of energy related to the square of the difference in their electronegativities In equation form, Pauling s formula (with units in kcal) is... 

When two atoms form a covalent bond, they do not share the electrons equally unless the atoms are identical. The concept of electronegativity was introduced by Linus Pauling to explain the tendency of an atom in a molecule to attract electrons. The basis for Pauling s... 

In Gordy s approach the ionic character of a single bond to chlorine equals one-half of the difference in electronegativities of the chlorine, 3.16, and the atom to which it is bonded. Thus the NQR frequency of this chlorine atom is a strong function of the Pauling electronegativity, Xp, of the atom M bonded to chlorine ... 

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