Atom

Definition

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

5 Must Know Facts For Your Next Test

1. The concept of the atom dates back to ancient Greek philosophers but was scientifically validated in the 19th century.
2. J.J. Thomson discovered the electron, leading to the plum pudding model of the atom.
3. Ernest Rutherford's gold foil experiment revealed that atoms have a dense, positively charged nucleus.
4. Niels Bohr proposed a model where electrons orbit the nucleus in discrete energy levels.
5. The Heisenberg Uncertainty Principle states that it is impossible to simultaneously know both the position and momentum of an electron.

Review Questions

• What discovery led to the downfall of J.J. Thomson's plum pudding model?
• How did Ernest Rutherford's gold foil experiment change our understanding of atomic structure?
• What does Niels Bohr's atomic model describe about electron behavior?

Related terms

Electron: A subatomic particle with a negative charge that orbits the nucleus of an atom.

Nucleus: The central part of an atom, composed mainly of protons and neutrons, and containing most of its mass.

Proton: A subatomic particle found in the nucleus with a positive charge equal in magnitude to that of an electron.