Atoms are the smallest units of matter that make up everything. All materials on Earth and in space are made of atoms. Each atom includes parts called protons, neutrons, and electrons. Atoms are extremely small and cannot be seen with the eye.

Different types of atoms are called elements, such as hydrogen, oxygen, and carbon. Atoms are found in air, water, rocks, and living things. They exist in all states of matter.

Atoms can join together to form molecules and compounds. These combinations make up many substances found in nature and everyday life. Atoms are the basic building blocks of all matter.