ABSTRACT
Liquids have roughly similar densities to solids, with typical values between half and twenty times that of water. The chapter describes a liquid as being like a disordered solid, but with a detailed structure which changes every few nanoseconds or so. Liquids are relatively under-studied in comparison with their solid relatives. The water molecule is much smaller than the ethanol molecule, and so should find it easier move through its liquid. However water experiences strong hydrogen bonding which slows down its motion in comparison with the weaker bonding of the ethanol. The data for organic liquids shows consistent relative magnitudes of the activation energies. The cell model provides a flexible framework for discussing processes in liquids. The optical properties of liquids may (for many purposes) be characterised by two parameters: the refractive index of the material and the absorbtion coefficient..
