Chemical reactivity theory Adam Wasserman Purdue University Chemical-reactivity theory (CRT) quantifies the tendency of atoms and molecules to react with each other. It can be formulated rigorously in terms of Kohn-Sham DFT and used to understand the early stages of chemical reactions. In this lecture I will explain the basics of CRT, define various indices of chemical reactivity including electronegativity, Fukui functions, local and global softness, and their corresponding kernels. I will discuss their significance, stressing the role played by derivative discontinuities of the exchange-correlation functional at integer electron numbers (introduced by W. Yang in a previous lecture).