Nucleus

Definition

The nucleus is the central core of an atom, containing protons and neutrons. It is positively charged and holds most of the atom's mass.

5 Must Know Facts For Your Next Test

1. The nucleus is composed of protons, which are positively charged, and neutrons, which are neutral.
2. The number of protons in the nucleus defines the element's atomic number.
3. Nuclear reactions, such as fusion and fission, involve changes to the nucleus and release significant amounts of energy.
4. In astronomical contexts, understanding nuclear reactions in stars helps explain their energy output and lifecycle.
5. Radioactive decay occurs when an unstable nucleus loses energy by emitting radiation.

Review Questions

• What particles make up the nucleus of an atom?
• How does the number of protons in a nucleus relate to an element’s identity?
• What role does the nucleus play in nuclear reactions?

Related terms

Proton:

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

Neutron:

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

Electron:

A subatomic particle with a negative charge that orbits the atom's nucleus.