Schomaker

Schomaker-StevensoD equation The equation a B = a + fl 0 09 (Xa - X ) relating the bond length to the individual radii rp and Tb of the two atoms concerned and the electronegativities Xp and X of the two atoms concerned in the bond. This relation is only empirical and is not very accurate. 

There is evidence from electron diffraction studies of pyrazine and pyridine that this value should be increased by 0.01 or 0.02 A because of the electronegativity of nitrogen (V. Schomaker and L. Pauling, paper to be published in Jour. Am. Chem. Soc.). 

For calculating the interatomic distance for a single bond, Ri, involving an atom of nitrogen, oxygen, or fluorine (or two such atoms), we use the equation of Schomaker and Stevenson namely... 

The discussion of interatomic distances in salts of oxygen acids of the second-row elements is presented in Table IV. In the first row of this table, below the names of the salts, there are given values of the electronegativity difference xa — xb, in the second row the sum of the single-bond radii, in the third row the Schomaker-Stevenson correction, and in the fourth row the single-bond interatomic distance. The next row contains the fractional amount of ionic character of the a bond, as given by the electronegativity difference with use of Table... 

The values of f (l) given in the table for electronegative atoms are their normal covalent single-bond radii28 (except for boron, discussed below). The possibility that the radius 0.74 A. of Schomaker and Stevenson29 should be used for nitrogen in the metallic nitrides should be borne in mind. 

Photo 13 Linus Pauling (right) with Prof. Verner Schomaker (SP 61), about 1960. 

For sphalerite and wurtzite, for example, the discussion of partial ionic character as described above for molyde-nite leads to the resultant average charges +0.67 for sulfur and—0.67 for zinc. The distribution of the sulfur atoms is calculated to be 12% S2 (quadricovalent), 50 percent S+, 32 percent S°, 6 percent S-, 0.2% S2-. The observed bond length 2.34 A with the sulfur radius 1.03 A and the Schomaker-Stevenson correction 0.05 A leads to 5 = 1.36 A for zinc (quadricovalent Zn2-). The increase by 0.05 A over the value 1.309 A for sp3 bonds of Zn° is reasonable as the result of screening of the nucleus by the extra electrons. 

Prof. Verner Schomaker Ph.D., Professor of Chemistry Emeritus, University of Washington, Seattle, Washington (deceased)... 

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