There are a number of fundamental concepts that are essential to know about in order to understand any account of modern chemistry. ‘Its principles: atoms and molecules’ describes, in very general terms, the nature of atoms and how they bond together in characteristic arrangements to form molecules and other fundamental types of compound. The Periodic Table, and its importance in the teaching of chemistry, is introduced. It summarizes relationships between the elements and plays a crucial role in organizing information about them. The structure of atoms—the nucleus, with its protons and neutrons, and surrounding electrons—is described along with ionic, covalent, and metallic bonding.