What is the name for the smallest units of all matter?

The smallest units of all matter are called atoms. Atoms are fundamental building blocks of matter that retain their chemical properties and can combine in various ways to form molecules and compounds. Each atom consists of a nucleus made of protons and neutrons, surrounded by electrons. This atomic structure defines the characteristics of different elements and is pivotal in chemistry and physics.

Molecules, while they represent combinations of atoms bonded together, are not the simplest unit of matter, as they consist of two or more atoms. Compounds are specific types of molecules composed of two or more different elements, and gases refer to a state of matter rather than the fundamental unit of matter itself. Therefore, atoms are correctly identified as the smallest units of matter, serving as the basic building blocks that make up everything we encounter in the physical world.