The valencies of the lanthanides vary more than was once thought. In addition to valencies associated with a half-full shell, there are valencies associated with a quarter- and three-quarter-full shell. This can be explained on the basis of Slater’s theory of many-electron atoms. The same theory explains the variation in complexing constants in the trivalent state. Valency in metallic and organometallic compounds is also discussed.

The basis of the Periodic Table is discussed. Electronic configuration recurs in only 21 out of the 32 groups. A better basis is derived by considering the highest classical valency (v) exhibited by an element and a new measure, the highest valency in carbonyl compounds (v*). This leads to a table based on the number of outer electrons possessed by an atom (N) and the number of electrons required for it to achieve an inert (noble) gas configuration (N*). Periodicity of (...) these is nearly complete. The new basis helps to settle the question of the best form of table and related issues. (shrink)

A new way of understanding entropy as a macroscopic property is presented. This is based on the fact that heat flows from a hot body to a cold one even when the hot one is smaller and has less energy. A quantity that determines the direction of flow is shown to be the increment of heat gained divided by the absolute temperature. The same quantity is shown to determine the direction of other processes taking place in isolated systems provided that (...) q is determined by the state of the system. Entropy emerges as the potent energy of a system [Σ], the potency being determined by 1/T. This is shown to tie in with the statistical mechanical interpretation of entropy. The treatment is shorter than the traditional one based on heat engines. (shrink)

The authors regret that there are errors in equation and subsequent discussion. The correct version is as follows.

The authors regret that there are errors in equation and subsequent discussion.

A modern version of Lewis’s theory of valency is presented. This takes account of the results of quantum–mechanical calculations on molecules. Topics covered are polar covalent bonds, hypervalency, coordinate bonds, nonintegral bonds, oxo-anions, variable valency among transition elements, and nonclassical compounds. A distinction is drawn between the valence shell of an atom and the Lewis shell. The concept of a fractional bond pair is presented.

A simple treatment of chemical equilibrium is given, based on Boltzmann’s distribution law. The results are compared with those obtained by using thermodynamics.

A simple way of introducing the theory of relativity to chemistry students is presented. This is based on experimental observations of the variation in the mass of an electron with speed. Analysis of these generates the equations chemists use, and provides a basis for critical discussion of the theory.

A statistical mechanical treatment is given of thermal contact between two systems. Reciprocal temperature emerges from this as the relative change in the number of microscopic states a macroscopic system at equilibrium ranges over, at constant volume and chemical composition, with change in internal energy. The significance of this is discussed in detail with reference to a monatomic gas and an Einstein solid.

This article presents a personal answer to the question “What is chemistry?”, set out in terms of six propositions. These cover “pure” and “applied” chemistry, different levels of description, and the broader context of chemistry.

The mole is a difficult concept. Surveys have shown that even many teachers do not have a proper understanding of it. To help to meet this problem, the SI/IUPAC formulation of the mole is carefully presented and explained. New SI proposals are also briefly discussed.