Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Atomic Mass Unit (amu/u) is a unit of measurement used to express the mass of atoms and subatomic particles. It is defined as 1/12th the mass of a carbon-12 nucleus.
Related terms
Carbon-12 nucleus: The carbon-12 nucleus is used as the standard reference for assigning atomic masses. It has a mass of exactly 12 atomic mass units.
Protons: Protons are positively charged subatomic particles found in the nucleus of an atom. They contribute to the overall mass and determine the element's identity.
Neutrons are neutral subatomic particles found in the nucleus of an atom. They also contribute to the overall mass but do not affect the element's identity.