In this book we provide a survey of the molecular structures of some 300 representative compounds of the main group elements, i.e. the elements in Groups 1 and 2, and 12 through 18. The emphasis is on their equilibrium structures, but some thermochemical parameters, particularly bond energies, are included when available. Most of the quoted structures have been determined in the gas phase, but crystal structures are included when gas phase structures are lacking, or when the change of phase is accompanied by a significant change of structure. The aim has been to organize the survey in a manner that brings out similarities and trends, and at the same time give adequate attention to those molecules that break well-established patterns.
Chemists use models to interpret and systematize information and to extrapolate from the known to the unknown. A good model is simple, has a wide validity range, and precise predictive power. However, since they all represent simplifications of a more complex reality, they will all fail in some instances. In this book we describe these models in parallel with the molecular structures for which they are most successful. The aim has been to provide a clear description of their physical basis, and to delineate the limits of their applicability.
During four decades of research on molecular structure and bonding, I have benefited from fruitful collaboration and innumerable discussions with fellow scientists in Norway and abroad. I wish, however, to express my particular gratitude to my colleagues at the University of Oslo, Professors Knut Faegri, Grete Gundersen, Trygve Helgaker, Svein Samdal, Tor Strand and Einar Uggerud; and to some of my students and postdocs, Richard Blom, Paul Kiprof, Kjell-Gunnar Martinsen, Kristin Rypdal, Wolfgang Scherer, Dmitry J. Shorokhov, Vasily I. Sokolov, Tatyana Strenalyuk, Andrey V. Tutukin, Natalya V. Tverdova, Hans Peter Verne, and Kari-Anne 0stby.
The information contained in this book has been collected by hundreds of scientists and published in hundreds, perhaps a thousand, articles. We do hope that the reader will accept that we have found it too cumbersome to give a complete set of references to the primary research literature. Instead we refer to widely available tabulations of structure data, thermodynamic data and atomic energy levels. Only when the original work is considered to be of exceptional importance or originality, when it is relatively recent, or when it may be particularly difficult to locate, have we included a full reference.
Finally: this is a book that I have wanted to write, and I should be delighted to learn that somebody has wanted to read it!