A sixth amendment?

Physical Chemistry

February 6, 1998

Composers of music are reputed to be superstitious about overstepping Beethoven's mark of a ninth symphony. For composers of physical chemistry textbooks, the equivalent mark may well be their fifth edition. When I was a student, the dominant physical chemistry text was Walter J. Moore's, for which the fifth was effectively the final edition. After that, physiccal chemistry has almost completely adopted Peter Atkins's version as the standard text. It is possible that Atkins is scanning the field for a challenger as the bookshop shelves wait for his recently announced sixth edition.

So what of this new addition to the field? Right from the opening chapter, Donald McQuarrie and John Simon throw up a surprise with an ambitious departure from traditional approaches. Almost all existing texts begin with material designed to connect with pre-college chemistry: states of matter, the kinetic theory of gases and then equilibrium thermodynamics. This is all "classical" matter, based on Newton's laws of motion and formulated in the 19th century. Often this will occupy anything up to ten chapters and perhaps 200 pages. Physical Chemistry: A Molecular Approach has none of this. It takes the brave position that the molecular world is quantum mechanical at heart and so a 21st-century text must begin there.

The first chapter is there to unsettle the cosy classical view and to shake students from their existing preconceptions. It deals with the failures of 19th-century physics - with black-body radiation, the photo-electric effect and spectra, particles with wavelength and the uncertainty principle. The "physical chemistry" chapters are interspersed with "MathChapters": the first of these follows chapter one immediately and addresses the issue of complex numbers. Again, the authors are taking no prisoners. But this molecular basis does allow a very coherent and logical development of physical chemistry. Over the first ten chapters, the authors build up through simple aspects of spectroscopy to chemical bonding, arriving at modern computational methods in chapter 11 - 450 pages of quantum mechanics right from the start. Symmetry and three chapters on more advanced spectroscopy then follow, with lasers featuring prominently in chapter 15. Somewhat surprisingly, the authors tackle dynamical processes of energy transfer at this stage where other texts usually place this more advanced aspect of kinetics.

It is not until chapter 16, some 630 pages into the book, that we reach ideal gases and then go on to find thermodynamics. Even here there are surprises. Having dealt with energy levels so well, the authors can use a molecular approach here too and so begin with the Boltzmann equation even before addressing the first law. Entropy is thus immediately interpreted in terms of spreading over energy levels - much more satisfactory than as an infinitesimal heat flow divided by temperature. There follows a fairly familiar development through to phase equilibria and then to chemical reactions. This always seems a stumbling point in physical chemistry teaching. We (properly) spend a long time building the foundations but this means dealing with basically unreacting systems when the exciting things in chemistry always seem to involve making new products in reactions. Kinetics takes its bow on page 1,047, and the book finishes with a short discussion of solids and surface chemistry.

There are some surprising omissions: no substantive mention of polymers or of colloidal systems, micelles or liquid crystals. Modern methods in these areas exploit the sort of statistical mechanical approaches on which one might have expected these authors to write with authority and enthusiasm. There is no electrochemistry. The kinetics section addresses gas-phase reaction dynamics but other areas such as oscillatory reactions and chemical pattern formation are not addressed. There is no mention of branched chains, such as the classic hydrogen + oxygen reaction, or such modern features of interest as the greenhouse effect, which is surely an excellent example of physical chemistry principles in action. Modern aspects of surface science and heterogeneous catalysis do not feature as prominently as in other texts. In many respects, this seems more like a chemical physicist's text rather than a physical chemist's. I am also slightly dismayed that the authors follow the American approach in dealing with pressure units, standard quantities and equilibrium constants, yielding some dimensional inconsistencies that can easily be avoided by working with standard equilibrium constants - an area where Atkins is exemplary.

The authors have been brave and I applaud their courage and intellectual honesty. There is great value in an alternative approach. They set high standards and many of us, as teachers and professionals in physical chemistry, will find inspiration in, and have our aspirations raised by, this text. It is beautifully produced, with clear diagrams and nice touches, such as the short biographies of scientists that appear between chapters. The publisher has done well to produce such a bulky hardback at a reasonable price. There are worked examples in the text, although students will always appreciate more than are provided. The problems set at the end of each chapter are fairly traditional but numerical answers without any significant explanation are provided at the end of the book. There are no significant compilations of data. In many respects, this is the sort of text many of us wish we could use in our teaching, harking back to some (probably non-existent) golden era.

In the United States, and where students have taken a sufficiently firm general chemistry and physics course before coming to their physical chemistry, McQuarrie and Simon's book will be a genuine option. In the UK, where we traditionally begin physical in the first week of the first semester, along with inorganic and organic, and where we have in many cases lost support in mathematics and physics, I suspect this book will frighten the many students who need to be coaxed through the more quantitative aspects. I will recommend this as a reference text to our third- and fourth-year students, to be consulted in conjunction with more specialist monographs, for our bonding and quantum mechanics modules and, particularly, for the dynamics section, where there is no obvious competitor at the moment.

Stephen K. Scott is head of physical chemistry, University of Leeds.

Physical Chemistry: A Molecular Approach

Author - Donald A. McQuarrie and John D. Simon
ISBN - 0 935702 99 7
Publisher - University Science Books
Price - £24.95
Pages - 1,0

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