Van Arkel—Ketelaar triangles

Abstract An equilateral triangle with vertices designated metallic (M), ionic (I), and covalent (C) was introduced for pedagogical reasons many years ago by van Arkel and Ketelaar to qualitatively catalogue the types of chemical bonding organized by the Periodic Table. These triangles display a sequence of atoms from left to right (M to C) in the Periodic Table along one side and binary combinations of atoms along the other two sides (MI and IC), and we have systematically extended the information content and usefulness. By the positioning of atom pair combinations according to the sum and difference of configuration energies, CE (the average ionization energy of the valence electrons of an atom). This permits division of the triangle into regions corresponding to metallic, ionic, and covalent bonding and, in effect, quantifies the Periodic Table. Very recently Professor Gordon D. Sproul of the University of South Carolina, Beaufort, found literature references on several hundred binary compounds previously determined to be bound as metallic, ionic, or covalent compounds, and cleanly separated these into their known bonding categories by use of CE with plots which give essentially the same dividing lines that we have derived theoretically.