Atom

Definition

An atom is the smallest unit of an element that retains the properties of that element. It consists of a nucleus containing protons and neutrons, surrounded by electrons.

5 Must Know Facts For Your Next Test

1. Atoms are composed of three primary particles: protons, neutrons, and electrons.
2. The atomic number of an atom is defined by the number of protons in its nucleus.
3. Isotopes are atoms of the same element with different numbers of neutrons.
4. Electrons occupy specific energy levels or orbitals around the nucleus.
5. The concept of atoms was first proposed by ancient Greek philosophers like Democritus but was later developed into modern atomic theory by scientists such as John Dalton.

Review Questions

• What are the three primary particles that make up an atom?
• How do isotopes of an element differ from each other?
• Who were some key historical figures in the development of atomic theory?

Related terms

Proton: A positively charged particle found in the nucleus of an atom.

Neutron: A neutrally charged particle found in the nucleus of an atom.

Electron: A negatively charged particle that orbits the nucleus of an atom.