Electrons and Chemical Bonding

Abstract

THIS BOOK WAS DEVELOPED from my lectures on chemical bonding in Chemistry 10 at Columbia in in the spring of 1962, and is mainly intended for the undergraduate student in chemistry who desires an introduction to the modern theories of chemical bonding. The material is designed for a one-semester course in bonding, hut it may have greater use as a supplementary text in the undergraduate chemistry curriculum. The book starts with a discussion of atomic structure and proceeds to the principal subject of chemical bonding. The material in the first chapter is necessarily quite condensed and is intended as a review. (For more details, the student is referred to R. M. Hochstrasser, Behavior of Electrons in Atoms, Benjamin, New York, 1964). Each chapter in the bonding discussion is devoted to an important family of molecules. Chapters II through VII take up, in order, the principal molecular structures encountered as one proceeds from hydrogen through the second row of the periodic table. Thus, this part of the book discusses bonding in diatomic, linear triatomic, trigona1 planar, tetrahedral, trigonal pyramidal, and angular triatomic molecules. Chapters VIII and IX present an introduction to modern ideas of bonding in organic molecules and transition metal complexes. Throughout, our artist has used small dots in drawing the boundary-surface pictures of orbitals. The dots are intended only to give a pleasing three-dimensional effect. Our drawings are not intended to be charge-cloud pictures. Charge-cloud pictures attempt to show the electronic charge density in an orbital as a function of the distance from the nucleus by varying the "dot concentration." The discussion of atomic structure does not start with the Schrödinger equation, hut with the Bohr theory. I believe most students appreciate the opportunity of learning the development of atomic theory in this century and can make the transition from orbits to orbitals without much difficulty. The student can also calculate several important physical quantities from the simple Bohr theory. At the end of the first chapter, there is a discussion of atomic-term symbols in the Russell-Saunders LSMLMs approximation. In this book the molecular orbital theory is used to describe bonding in molecules. Where appropriate, the general molecular orbitals are compared with valence-bond and crystal-field descriptions. I have written this book for students who have had no training in group theory. Although symmetry principles are used throughout in the molecular orbital treatment, the formal group-theoretical methods are not employed, and only in Chapter IX are group-theoretical symbols used. Professor Carl Ballhausen and I are publishing an introductory lecture-note volume on molecular orbital theory, which was written as a slightly higher level than the present book. The lecture notes emphasize the application of group theory to electronic structural problems. The present material includes problems integrated in the text; most of these are accompanied by the worked-out solutions. There are also a substantial number of problems and questions at the end of each chapter. It is a great pleasure to acknowledge the unfailing support, encouragement, and devotion of the seventy-seven fellows who took the Columbia College course called Chemistry 10 in the spring of 1962. I doubt I shall ever have the privilege of working with a finer group. The class notes, written by Stephen Steinig and Robert Price, were of considerable help to me in preparing the first draft. I would like to thank Professors Ralph G. Pearson, John D. Roberts, and Arlen Viste for reading the manuscript and offering many helpful suggestions. Particularly I wish to thank one of my students, James Halper, who critically read the manuscript in every draft. Finally, a large vote of thanks goes to Diane Celeste.

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