ABSTRACT
Since atomic structure is covered in introductory chemistry courses, the student should be aware by now that the atom consists of a nucleus containing neutrons and protons around which electrons orbit, the orbits being more or less confined to certain radii. (We will not be concerned here with the subatomic particles such as quarks or neutrinos.) The smaller the diameter of the orbit, the greater the attractive force between the electron and the nucleus and the greater the absolute binding energy (BE). Binding energies, by convention, are considered to be negative, so we are speaking of a large negative binding energy for the innermost orbit. The electrons in the outer orbits are bound less tightly, and the outermost electrons can to some extent be considered to be loosely bound and not necessarily residing in well-defined orbits. These are the valence electrons and are the ones that are involved in the bonding together of the atoms, and hence strongly affect all material properties: physical, mechanical, and chemical. The nature of this bond is what determines whether the substance is a metal, in which the bond is often between like atoms, or a ceramic or a polymer material, where the bond is between dissimilar atoms. Before describing these various bond types, we review the electron configuration and the related periodicity of the elements.
