Protons

Definition

Protons are positively charged subatomic particles found in the nucleus of an atom. They contribute to the atomic number and, therefore, the identity of an element.

5 Must Know Facts For Your Next Test

1. Protons have a positive electric charge of +1e or approximately $1.602 \times 10^{-19}$ coulombs.
2. The number of protons in an atom's nucleus is called its atomic number and defines the element.
3. Protons are composed of three quarks: two up quarks and one down quark.
4. Protons have a rest mass of approximately $1.6726 \times 10^{-27}$ kilograms, making them slightly less massive than neutrons but much more massive than electrons.
5. In a neutral atom, the number of protons equals the number of electrons.

Review Questions

• What is the charge and approximate mass of a proton?
• How does the number of protons in an atom's nucleus relate to its atomic number?
• What quarks make up a proton?

Related terms

Neutron:

A neutrally charged subatomic particle found in the nucleus, with a mass slightly greater than that of a proton.

Electron:

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

Atomic Number: The number of protons in an atom's nucleus, which determines the chemical element.