What is the smallest unit of matter?

The smallest unit of matter is an atom. Atoms are the basic building blocks of all matter, and they consist of protons, neutrons, and electrons. Each element in the periodic table is made up of one type of atom, which determines its properties and behavior in reactions.

Molecules, although they are fundamental structures, are formed when two or more atoms bond together. An element is a substance made up entirely of one type of atom, and while "particle" can refer to various tiny components in physics, it is not a precise term for the smallest unit of matter in chemistry. Thus, understanding that an atom is the foundational unit helps to comprehend the larger structure of matter, from elements to complex molecules.