Atomic Radii. I

The Physical Meaning of Bragg's "Atomic Spheres" and "Atomic Radii."—W. L. Bragg's "atomic spheres" and "atomic radii," considered in the light of the Lewis theory of atomic and molecular structure, have a definite physical meaning. The "atomic sphere" of an atom is its valence shell, and its "atomic radius" is the distance from atomic center to a group of electrons (usually an electronpair) in the valence shell. This idea is applied to several crystals.

Bragg's Method of Calculating Atomic Radii not always Valid.—Bragg's assumption that the distance between two adjacent atomic centers equals the sum of their radii is often not valid, since in many cases the group of electrons constituting the bond does not lie on the line joining the atomic centers; in other words, the two atomic "spheres" overlap.

Factors Affecting the Atomic Radius.—The various factors affecting the distance from atomic nucleus to valence group—the atomic radius—are discussed, with examples.