Lewis-Langmuir atomic charges

A R = Allred and Rochow BPI = bond polarity index CE = configuration energy DHF = Dirac-Hartree-Fock DHHF = Dirac-hyper-Hartree-Fock El = energy index FC = formal charge LLa = Lewis-Langmuir atomic charges ON = oxidation number OS = oxidation state. 

Figure 14 Lewis-Langmuir atomic charges. Top examples using the simplest formulation. Middle plot of the electronegativity ratio that interpolates between fonnal charge and oxidation number. The dotted line is the formal charge limit and (0,0) is the oxidation number limit. Bottom improved LLa formula that corrects for charge on nearest neighbor atom...

Molecular Properties. Corresponding to its nuclear charge number, the nitrogen atom possesses seven shell electrons. One electron pair in in the ground state 1 s(K shell), and five electrons are distributed over the four orbitals with the principal quantum number 2 (L shell). Of these, one electron pair occupies the 2 s level and three unpaired electrons, respectively, a half of the remaining three levels, 2 px, 2 pv, 2 pz. The unpaired electrons can enter into electron-pair bonds with the 1 s electron of three hydrogen atoms. Thus, the three half occupied orbitals of the L shell become about fully accupied (formation of an octet of the neon type in accordance with the octet theory of Lewis-Langmuir). 

Figure 15 Correlation diagram between Lewis-Langmuir and natural population analysis (NPA) charges for carbon atoms in 15 organic molecules a, acetone (Me) b, acetaldehyde (Me) c, acetonitrile (Me) d, ethane e, vinylamine (CH2) f, nitromethane (Me) g, vinylamine (CH) h, formaldehyde i, acetonitrile (CN) j, acetaldehyde (CO) k, acetone (CO) 1, difluoromethane m, formamide n, fluoroform o, carbon tetrafluoride...

For F3SN, the standard Lewis stractures are of types (21)-(23). These structures satisfy the Lewis-Langmuir octet rule, but each carries a formal charge of +2 on the sulphur atom. 

This absence of effect, Lewis considered logically and scientifically objectionable for that state of motion which produces no physical effect whatsoever may better be called a state of rest. [Lewis, 1916]. And he was not alone in his scepticism. J. J. Thomson was trying to work a static atom theory as late as 1923 as were Langmuir, Davey, Born, Lande and Parson. All involved were trying to modify Coulomb s force law to get a theory in which the electrons in an atom remained still and were distributed at the corners of a cube. But in his Nobel lecture in 1922, Bohr delivered a sharp attack on static atom theories, pointing out that Earnshaw s theorem showed that a static distribution of charges must be unstable if Coulomb s law applies and that the argument could be extended to cover the proposed modified potentials. 

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