Nucleus

Definition

The nucleus is the small, dense region at the center of an atom that contains protons and neutrons. It is responsible for most of the atom's mass.

5 Must Know Facts For Your Next Test

1. The nucleus was discovered by Ernest Rutherford in 1911 during his gold foil experiment.
2. Protons in the nucleus have a positive charge, while neutrons are neutral.
3. The number of protons in the nucleus (atomic number) determines the element of the atom.
4. Nuclear forces (strong force) hold protons and neutrons together within the nucleus despite their repulsive electromagnetic force between protons.
5. Isotopes are atoms with the same number of protons but different numbers of neutrons in their nuclei.

Review Questions

• Who discovered the atomic nucleus and through which experiment?
• What particles are found in the nucleus and what are their charges?
• How does the atomic number relate to the nucleus?

Related terms

Proton: A subatomic particle found in the nucleus with a positive electric charge.

Neutron: A subatomic particle found in the nucleus with no electric charge.

Isotope: Atoms of the same element with different numbers of neutrons in their nuclei.