ABSTRACT
Broadly speaking, the periodic variation of the bulk modulus of the lanthanide elements arises from the periodic variation in the amount of covalent bonding present. It is a surprising fact that the oscillation amplitudes of atoms in solids are never very large. The thermal expansivity of plastics is typically one order of magnitude or more greater than that of crystalline solids. In the Debye theory of the heat capacity of solids, the thermal energy of a solid is considered to be tied up in vibrations of the atoms of the substance. The detailed mechanism of dielectric breakdown in solids differs considerably from that in gases. In solids, electrons create a region which is hotter than the equilibrium temperature, making it considerably more likely that a new carrier will be formed locally. The optical properties of solids are rather difficult to characterise succinctly, since typically this requires a specification of their absorbtion and reflection across the optical frequency range.
