[Bonds].

Mechanical properties of bonds are discussed, with the aid of a simple phenomenological model in which the variation of energy as a function of distance between the elements is described in terms of polynomials. The properties of various kinds of bonds (ionic bond, metallic bond, covalent bond, van der Waals bond) are explained with the aid of simple models. Carbon is discussed with two examples: bonds between 60 atoms that lead to the formation of a three-dimensional molecule known as Buckminsterfullerene, and the alternative sheet-shaped configuration known as graphene, that has recently become the centre of interest. A general theory for finding the energy levels is introduced, relying on Feynman’s coupled wave equations. There is a brief reference to nuclear forces, followed by a discussion of the hydrogen molecule. The relationship between coupling and the splitting of the energy levels is discussed with an analogy to coupled resonant circuits.