Journal and Proceedings of
The Royal Society of New South Wales
Volume 119 Parts 3 and 4 [Issued May, 1987]
CONTENTS
| AUTHORS & TITLES | PAGES |
| Hyde, B.G., Inorganic and Mineral Structures Reconsidered (Liversidge Lecture 1986) | 153-164 |
| Abstracts of Theses [Opening in a new page] | |
| Seow, K.T.F.P., Pancreatic Fluid-and Electrolyte Secretion | 165-166 |
| Pascoe, Leigh, Fitness Components of Chromosomal Homozygotes in Drosophila melanogaster in Age Structured Populations | 167-168 |
| Walsh, Andrew, Photographic Measurements of Bubble Populations from Oceanic Whitecaps | 169 |
Vol. 119 Pts 3-4, pp.153-164
Inorganic and Mineral Structures Reconsidered
B.G. Hyde
[Liversidge Lecture delivered before the Royal Society of New South Wales, September 24th, 1986, at The University of Sydney]
Abstract. For 60 years or so the "Ionic Model" has been fundamental to solid state chemistry and mineralogy. It has been useful, but the ideas involved have become sacrosanct, even when they do not work! Quantum mechanical methods are becoming increasingly important and useful, but they lack the simple "physical" approach and, in any case, so far can only be applied to the simpler structures.
An alternative approach, as simple, naive and "physical" as the ionic model, is successful where the latter succeeds and where it fails (e.g. in silicates). It can often be useful for simple and complicated structures; and it avoids the ionic/covalent dichotomy. Like the successful quantum methods, it sees no difference in principle between non-molecular structures and those of small molecules (another unhappy dichotomy). It emphasises that, as in organic chemistry, one "size" for an atom is insufficient for understanding structure; at the crudest level one needs a bonding size (for first nearest neighbour interactions) and a non-bonding size (for second and further neighbours).
The usefulness of this alternative approach is demonstrated in several areas of interest, particularly to the chemist and mineralogist: in (a) determining crystal structures and coordination numbers therein, (b) its effect on the stability/instability (and even non-existence) of simple compounds such as binary oxides, nitrides and carbides, (c) leading to simple descriptions of the structures of some mundane compounds such as sulphates, silicates and carbonates, previously undescribed, but (d) often of interest to physicists because their structures may be incommensurably modulated, (e) accounting for the effect of high pressure on crystal structure.
It transpires that cations, far from being small in size and influence, often dominate crystal structure and behaviour.