atom Post author By ScotFagerland Post date July 12, 2022 The smallest unit of matter that is (usually) stable. It consists of a nucleus of protons and neutrons, surrounded by electron clouds. There are about 100 kinds of atoms, the elements of chemistry. Related Articles: Glossary: neutronGlossary: nucleosynthesisGlossary: protonO, Say Can You See?Glossary: electron ← potential energy → proton