Introduction

Atoms in a compound are held together by chemical bonds — the forces responsible for that binding. A chemical bond can form in one of two ways: by the loss and gain of electrons between two atoms, or by the two atoms sharing a pair of electrons. In either case, the driving idea is the same: each atom ends up with a more stable electronic arrangement afterwards, resembling that of the nearest noble gas. Only the electrons in an atom's OUTERMOST (valence) shell take part in bond formation — the inner, core electrons are too tightly held by the nucleus to be involved. This simple observation — that bonding is a valence-shell phenomenon aimed at a stable configuration — is the seed from which every theory in this chapter (Kossel-Lewis, VSEPR, valence bond theory, molecular orbital theory) grows, each adding more explanatory power than the last.