TABLE OF CONTENTS The triumph of quantum mechanics during the 1920s opened the door to a new understanding of a wide range of phenomena involving the most fundamental properties of matter and radiation, the fundamental constituents of the Universe. The new physics also enabled an amazing variety of technological applications that are continuing to transform our lives from lasers and microchip transistors to new medical imaging devices, and a host of new materials. Combined with relativity theory, quantum mechanics is the foundation for understanding the interactions of radiation and matter, the behavior of elementary particles at extremely high energies, and many of the stellar phenomena observed in cosmology. Soon after the formulation of quantum mechanics, scientists successfully applied the new theory to a new understanding of the nucleus of the atom that is still used today. This is discussed in Chapters 17 and 18. During the same period, scientists also utilized quantum mechanics to gain a new understanding of the structure and behavior of matter, including, in particular, the thermal and electrical properties of solids. These are the focus of the current chapter.
It was well known that matter appears in one of three states, or phases solid, liquid, and gas or vapor. According to the kinetic-molecular theory (Chapter 7), one factor distinguishing each of these states is the amount of energy distributed among the molecules making up the material. In the gaseous state, the molecules have the most energy and in the solid...
