ABSTRACT
This chapter explores how current theories of molecular structure lead to an understanding of the strengths of bonds and other physical properties of organic compounds. The principles of thermodynamics relate the effective concentration of chemical species in equilibrium to the enthalpies and entropies of those species. Bond energies, closely related to enthalpies, have precise values, which may be measured, but thermodynamic principles give no information about the origin of these bond energies. The higher boiling point of ethanol is a reflection of the greater intermolecular forces between molecules. Since ethanol has a hydrogen atom attached to an electronegative oxygen atom it is able to form hydrogen bonds; this is not the case with dimethyl ether, which, therefore, has a lower boiling point. Both boron and aluminium are in group three of the periodic table and, as such, form compounds that have only six electrons in their outer valence shell.
