Tutorial Chemistry Texts, No 5. The Royal Society of Chemistry: London, 2001. 181 pp. Figs., tables. ISBN 0-85404-647-X. $15.00.

On my bookshelf are two earlier books by Jack Barrett: Introduction to Atomic and Molecular Structure, published in 1970, and Understanding Inorganic Chemistry, published in 1991. I have always liked his treatment of the bonding in the water molecule, and so I naturally turned to the discussion of the water molecule in this new book, Section 5.3.1, pp 94-100. The treatment is very tight, including a comparison between the bent and the hypothetical linear molecule. The results of the MO treatment are supported by a photoelectron spectrum of water vapor. Barrett shows how symmetry properties determine which atomic orbitals can combine to give bonding molecular orbitals; that the p orbital perpendicular to the H-O-H plane is nonbonding in character; and (most important) that the energy gap between the 2s and 2p orbitals on oxygen is so large that the 2s orbital is essentially nonbonding. The level of the treatment of bonding is thus clearly defined: this is not for freshmen, but for sophomore to senior students. (In fact the approach is similar in flavor to that in Inorganic Chemistry by Miessler and Tarr.)

Chapter 1 takes the student through a very condensed treatment of Bohr atom, atomic orbitals, quantum numbers, and electron configurations. Only Allred-Rochow electronegativity coefficients are considered (p 13) on a 3-dimensional bar graph, but with no table of numeric values.

The heart of the book begins with Chapter 2, Molecular Symmetry and Group Theory. The pedagogical aims are clearly stated. The diagrams are clear and attractive, some in two colors. There is a good section of Worked Problems, plus further problems (whose answers are at the end of the book). This is clearly meant to be a text for the student to use and learn from. (There is a minor cultural problem in one question about point groups on page 32: the object is a rugby ball.)

Diatomic molecular orbitals are treated conventionally, with energy data from photoelectron spectra to support the results of the MO treatment (e.g. data for N₂ and CO in Table 4.3). The photoelectron spectra themselves are not given, which I feel is an unfortunate omission.

VSEPR is revised in two pages. The MO treatment of CO₂ and XeF₂ is discussed in some detail and is followed by that of NO₂⁺, NO₂, NO₂^-. Barrett very explicitly points out how the s-p energy gaps on the atoms govern the extent of orbital mixing no matter what the symmetry properties may indicate: an important point.

Chapter 6 is about Covalent Bonding in polyatomic molecules; it incorporates VSEPR, point group symmetry, and molecular orbitals. Although the MO treatment of methane is covered very tersely, it is supported by a good figure of methane's photoelectron spectrum. The bonding and shapes of BF₃, NF₃, and ClF₃ are discussed nicely. The terms HOMO and LUMO are used (p 134); I could find neither term in the index but they are defined on p 101.

There is an interesting and unusual use of the VSEPR approach to predict the molecular shapes of products of successive dehydration reactions (Figs. 6.18 to 6.21).

Chapter 7 deals with metallic and ionic bonding. The ionic-covalent transition is discussed in terms of Fajans' rules. There is a reference to Pyykkö's Chemical Review of 1988 about relativistic effects but not to his later Review of 1997.

One must now ask: what is the place for this book?

It is not meant to be a comprehensive text about bonding in molecules: for example, ozone is not mentioned nor are the two singlet forms of dioxygen. It is part of the RSC series of Tutorial Texts aimed at first- and second-year students in British universities, who have completed the UK A-level syllabus. The text is very compressed. A student would profit by reading it after a more leisurely introduction during lectures. A lecturer who knows the subject will gain some new ideas and insight from a different point of view. It is well worth having a copy in your library.