Schomaker-Stevenson relationship

The Schomaker-Stevenson relationship proposes that such bond shrinkage is directly proportional to the electronegativity difference between the bound atoms and that the interatomic distance, rA B, is thus linearly related to the covalent radii, ta and r ... 

The Schomaker-Stevenson relationship states that heteropolar bonds are always stronger and shorter than hypothetical, purely covalent bonds between the same atoms. In an ionic crystal, would you expect some covalency to shorten or lengthen the bond Explain. (Shannon, R. D. Vincent, H. Sirtict. Bonding (Berlin) 1974. 19, I.)... 

XVa<->b) (two similar ionic forms). They therefore proposed an equation known as the Schomaker-Stevenson relationship which takes account of this by making the bond distance depend on the electronegativity difference, which is an index of the ionic character of the bond. The equation they suggested is... 

The best fit is obtained with the constant c = 8.3 pm and the normal bond radii listed in Table 6.3. These radii and the modified Schomaker-Stevenson (MSS) relationship. 

When two atoms of different electronegativity are connected by a covalent bond, the bond length is always shorter than the sum of the individual homoalomic covalent radii for the atoms in question. The shortening is proportional to the difference in electronegativity of the two elements and is expressed by the relationship due to Stevenson and Schomaker. 

Table 11 gives standard covalent radii for most of the elements of the periodic table. Most of these have been calculated from the best data available in the literature using the considerations of paragraphs 1 -3 above. Thus when radii or the appropriate multiplicity and hybridization are added and corrected for difference in electronegativity by the Stevenson and Schomaker relationship, the observed bond length will be obtained. For example, the O-F bond in OF would have the value 0.745 + 0.709 — 0.910.5) = 1.409 A. The experimental value is 1.41 A. 

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