Atomic mass unit
The atomic mass unit (u) is a unit of mass defined as exactly one twelfth the mass of a neutral carbon-12 atom in its ground state.
Carbon-12: Carbon-12 is the stable carbon isotope with six protons and six neutrons. Its atomic mass defines the atomic mass unit by convention.
Unified atomic mass unit: The unified atomic mass unit, symbol u, is defined as one twelfth the mass of a carbon-12 atom. It is the standardized name and symbol for the unit defined here.
Molecular mass: Molecular mass is the mass of a molecule, usually expressed in daltons or atomic mass units. Adding constituent atomic masses gives a molecule’s mass in this unit.
Atomic weight: Atomic weight is the relative atomic mass of an element in a specified sample, expressed as a dimensionless ratio. It is often confused with atomic mass, but it is not a mass unit.
Isotope: An isotope is a form of an element whose atoms have different numbers of neutrons. Isotopes explain why an element’s atoms can have different masses.
Dalton (unit): The dalton, symbol Da, is a non-SI unit of mass equal to one unified atomic mass unit. It is an alternative name used especially in chemistry and molecular biology.
Molar mass: Molar mass is the mass of one mole of a substance, commonly expressed in grams per mole. Its numerical value in g/mol closely matches particle mass in u.
Gram: The gram is a metric unit of mass equal to one thousandth of a kilogram. It suits laboratory-scale quantities, whereas the atomic mass unit suits individual particles.
Atomic mass: Atomic mass is the mass of an individual atom, commonly expressed in atomic mass units. It is the quantity commonly measured using this unit.
Kilogram: The kilogram is the SI base unit of mass. The atomic mass unit has an experimentally determined value in kilograms.