An atom is the smallest unit of ordinary matter that forms a chemical element. Atoms are extremely small, typically around 100 picometers across.
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of protons and neutrons.
Electrons are subatomic particles with a negative electric charge. They are found outside the nucleus in regions called orbitals or electron shells.
Electrons play a crucial role in chemical bonding between atoms as their interactions determine many of the properties of matter.