What is tetrahedral covalent radius?

Answer 1

Consider an A-B bond in a crystal, where both the atoms A and B have four neighbours in a tetrahedral arrangement. The simplest examples include Group-14 elements (diamond, silicon) and binary AB compounds (ZnS, GaAs). There also are more complicated structures, such as the three-element chalcopyrites (CuInS2) or the four-element kesterites and stannites (Cu2ZnSnS4). Now, the idea is to statistically fit a set of such bond lengths, R, to a set of tetrahedral covalent radii, r(A), for each element, A:

R(AB) = r(A) + r(B). (1)

Such fits were published by Pauling and Huggins (1934) or Van Vechten and Phillips (1970). The latest fit of subpicometer statistical accuracy for 30 elements in 48 compounds was published in January 2012.

Answer 2

The tetrahedral covalent radius refers to the distance from the nucleus of an atom to the outermost electrons when the atom is bonded in a tetrahedral arrangement. It is a measure of the effective "size" of the atom in a covalent bond where the electron pairs are arranged in a tetrahedral geometry. This radius is used to estimate the bond lengths in molecules with tetrahedral geometry.