Atomic mass unit (u)

Definition

The reference unit for atomic mass, defined so that a Carbon-12 atom has a mass of exactly 12 u.

Atomic mass is essentially the count of protons plus neutrons, since electrons contribute about 1/1836 the mass of a proton and are negligible. Carbon-12, with six protons and six neutrons, was chosen as the basis, so hydrogen with one proton is about 1 u. Numerically the atomic mass unit equals the molar mass in grams per mole, which is the core translator between the atomic and bulk worlds.

Related concepts

Atomic mass and atomic weight · Isotopes · Mole

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Part of The Blueprint of Water · 📏 measurement