Atomic mass and atomic weight

Definition

Atomic mass is the mass of a single atom, while atomic weight is the abundance-weighted average mass across an element’s naturally occurring isotopes.

Nearly all of an atom’s mass sits in the nucleus because electrons weigh about 1/1836 as much as a proton. Because isotope proportions are stable and predictable, atomic weight behaves as a fixed constant for field work. For molar mass, dosage, and stoichiometry the difference between the two is negligible, so the book uses the terms interchangeably.

Related concepts

Mole · Molar mass · Atomic mass unit (u)

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Part of The Blueprint of Water · 📏 measurement