To understand the scientific principles that underlie any observable phenomenon in our world (Fig. 1.1), we have to take a look at the nature of chemical bonds and molecular interaction forces that determine the behaviour of all matter at the submicroscopic level. Because the underlying concepts are highly complex, chemists have resorted to the use of models that make the structure of atoms, molecules and their interaction understandable. These models are used in chemistry textbooks. Of course, one must remember that models necessarily simplify complex scientific ideas so that some of their essential features are highlighted for the discussion of a particular problem. In the following introduction, the focus will lie on those aspects of chemical bonding and molecular forces that play an important role in the interaction of different molecules, particularly water and cellulose. More detailed information on these chemical principles, especially as they concern the nature of chemical bonding, can be found in the selection of textbooks that were drawn upon for this review and that are listed in the references.

The field of chemistry is basically concerned with the structure and transformation of matter, i.e. the material substance that constitutes the universe. Because all matter is composed of atoms or molecules, the science that aims at explaining it must focus on the submicroscopic level. At this level, the causes of the behaviour of material substances are explained by the behaviour of atoms, molecules and the electrons that are part of the atomic structure. In other words, chemistry is a science that describes the mechanisms by which material substances or reactants come into intimate contact with each other so that they are transformed into new products. Macroscopically, we observe material changes with the naked eye. We notice, for example, when a polished steel plate corrodes because its smooth and shiny surface is marred by the formation of brown rust encrustations. When paper ages, we notice its discolouration and loss of its mechanical strength. Such alterations we observe macroscopically. They result from changes in the material structure that occur at the atomic or molecular level where chemical bonding and elemental composition take effect. Thus chemistry is a tool to explain these observations on a molecular or microscopic scale and to relate them to the macroscopic world.

Munowitz (2000) describes the atom as an electrical entity, in other words an entity that consists of electrically charged particles. The electric charge is a fundamental property that enables matter to interact by way of complementary electrical forces. Charge can be positive or negative. Particles of opposite charge are forced together by