This document provides an overview of band theory in chemistry. It defines band theory and describes the different types of bands including conduction bands and valence bands. It explains how band structures differ in insulators, semiconductors, and conductors. Semiconductors have a small band gap that allows electrons to jump between the valence and conduction bands when heated. There are intrinsic and extrinsic types of semiconductors depending on whether impurities have been added. Band theory is important for understanding chemical bonding, material properties, and applications in electronics.