Electron Population and Net Charge of Center

Notice that Q is negative if the population of A, PA, exceeds the number of electrons required to give a neutral center. It is easily verified that 

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Chemical bonds have an important effect on the property of the materials. Covalent and ionic bonds, the main composition of the chemical bond, are discussed. The ionic bond is much like the Coulomb force. It is inversely proportional to the distance between atoms and directly proportional to the atomic net charge. The net charge is expressed as the difference between the atomic number and the electronic population. The net charge average values of the center atoms of every model are... 

Table 23.2 shows the net charge of the center lithium ion and the bond overlap population between the center lithium ion and neighboring halide ions obtained for model II. The net charge values decrease with increasing atomic number of halide ion. On the other hand, the bond overlap population values are almost identical. This is probably due to increased electronic charge around the lithium ion. 

The above arguments form the core of Mulliken s population analysis [83], and it is customary to call the atom-centered electrons the (atomic) net populations (NP) which, together with the overlap populations (OP), add up to the total electron number in the above example, this is 2 = NPi + NP2 + OP = 0.61 + 0.61 + 0.78. We might also cut the overlap population s)nnmetrically and add each half to the net populations, thereby defining (atomic) gross populations (GP) in the H2 example, this makes 2 = NPi + j x OP + NP2 + x OP = GPi + GP2 = 1.00 + 1.00 = 2, which is very simple. Within this scheme, the atomic charge Cj is the difference between the atomic number Z and the gross population cj = Z — GP = 1.00 - 1.00 = 0) such that the H atom is neutral in the H2 molecule, as expected. 

The population analysis of the wave function obtained by a quantum-chemical calculation allow to assign atomic charges q (or net atomic charges) and evaluating bond orders. The charges measure the extent of electronic density localization in a molecule. Negative q values mean that excess electronic charge is at center a while positive values mean that center a is electron-deficient. 

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