Electric and Magnetic Properties

Abstract

A molecule is the most elementary unit of a substance which still retains the intrinsic nature or function of that substance. Molecules are composed of atoms, but the nature of a molecule is usually very different from that of the component atoms. On the other hand, the nature or function of a molecular solid is primarily determined by its constituent molecules in the zero-order approximation. The structure and properties of molecules in a condensed state are usually very similar to those in the isolated state. The differences between the two states are sometimes very small but are sometimes significantly large. The degree of these differences depends on the interactions between the molecules in the condensed phase. The main intermolecular interaction is usually of the van der Waals’ type, which is much weaker than valence bond or ionic interactions. A weak interaction between molecules leads to a large separation between molecules, and as a consequence electrons are usually localized inside a molecule even in the condensed phase.