3.0 INTRODUCTION The advances in modern electronics engineering have been made possible by the achievements in the study of the structure of materials. This has, for instance, made it possible to come up with high quality conductors and insulators for very high voltage transmission. The development of semi-conductor technology has brought rapid changes in the way electricity is used. This chapter is devoted to the study of the elementary structure of materials and their electric properties. It serves as a basis for the study of the sources of electricity and the behaviour of electric circuits. 3.1 Atomic Theory Definition Matter is anything that has weight and it occupies space. It exists in three forms: (a) Solid. (b) Liquid. (c) ...