This month's cover provides full-color versions of all of the figures in the paper by Shusterman and Shusterman that begins on page 771. The authors provide a convincing rationale for using two- and three-dimensional models of atomic, ionic, and molecular electron density in teaching both general and organic chemistry. They use such models to teach atomic and molecular size; ionic, covalent, and polar-covalent bonding; multiple bonding and bond order; electron delocalization; acid-base behavior and intermolecular forces, including hydrogen bonding between DNA base pairs. The figure illustrates an electrostatic potential model for the interaction between guanine and cytosine that shows clearly how regions of high electrostatic potential in guanine match with regions of low electrostatic potential in cytosine, and vice versa.

Several articles deal with the relationship between structure and activity, particularly of medicinals and drugs, extending the idea of electron density as a factor in molecular science. Schatz brings together several papers from other journals that relate the effects of various compounds on brain chemistry (page 746). It seems that some of these may literally be food for thought, and their similarities in structure and electronic structure are quite interesting. A closely related paper by Agosta that begins on page 857 describes a number of drugs and medicines derived from plants and provides insights into their use by humans. For more on this subject, see Agosta's book, which is part of our summer reading list (page 748). On page 855, Hickman and Neill describe a simple laboratory activity that models absorption of drugs via the gastrointestinal tract.

As usual we have a number of book and software reviews beginning on page 764. These include chemistry under extreme conditions, reference software for IR spectra of organic molecules, biological and chemical warfare, and history of scientific research. In addition, in honor of summer and the leisure it brings to at least some academics, book review editor Ed Walsh and several others have recommended interesting and informative books that you may want to take along for reading pleasure on your vacation. The summer reading list begins on page 748 and includes personalities (Ingold, Bader), molecular design, the environment, chemical warfare among animals and plants, chemistry and language, scientific revolutions, science literacy, chemical education, and the flight from science and reason. There is truly something here for everyone.

The subject of solids is approached from a number of directions this month. On page 785, Gulden et al. describe a materials science teaching module that can be incorporated into any introductory course, whether at the high school or college level. Cady (page 794) provides a visible, colorful, and inexpensive way to model cubic unit cells using pom pons. Liang has developed an inexpensive kit for constructing models of crystals that is based on multiwell tissue-culture Petri dishes. The kit is described on page 795. The symmetry properties of crystal lattices are more complex than those of individual molecules, and hence more difficult to teach. On page 797 Hardgrove shows how a carefully designed series of exercises can help students learn about space-group symmetry. When chiral molecules crystallize the crystals they form can be chiral, a fact discovered by Louis Pasteur. Suh et al. recount Pasteur's famous separation of enantiomeric crystals of sodium ammonium tartrate as part of an overview of chirality that includes crystal symmetry. Turn to their article, beginning on page 800, to find out how many of the 230 space groups are compatible with crystallization of a pure chiral substance, and how many can accommodate nothing but chiral molecules.

Three other papers (pages 806Ð812) deal with symmetry, but for point groups. Baraldi and Vanossi derive the character tables of all finite point groups in rigorous fashion. McNaught deals with reducing representations in an infinite point group, and in a separate paper examines the four different character tables extant for the group Dinfiniteh, showing that some have different operations and others have different characters for the same operation.

Two papers this month describe labs in which students are encouraged and expected to behave more like scientists. May and Gupta report on an electrochemistry discovery course, mainly lab based, that encourages undergraduates into undergraduate research. Kharas (page 771) describes a sophomore organic laboratory that is investigative in nature and involves individual student research projects in organic and polymer chemistry. Both of these papers reflect the trend for laboratories to become more open-ended and for students to have more responsibility for discovering chemistry themselves.