Moving four columns to the right puts element under Pb and in group IVA. Parte 1 de 4 Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or instructional purposes only to students enrolled in courses for which the textbook has been adopted. The Cl- ion is a chlorine atom that has acquired one extra electron; therefore, it has an electron configuration the same as argon. Atomic mass is the mass of an individual atom, whereas atomic weight is the average weighted of the atomic masses of an atom's naturally occurring isotopes. Solve for r in terms of A, B, and n, which yields r0, the equilibrium interionic spacing.