atomic weight
Scientific term used in chemistry; refers to the average mass of atoms of an element, taking into account the relative abundance of isotopes.
The atomic weight of hydrogen is about 1.008.
Atomic weight is calculated taking into account the relative abundance of isotopes.
分子量 (molecular weight) is the sum of the atomic weights of all atoms in a molecule.
Compound of 原子 (atom) and 量 (quantity, weight). A straightforward calque from Western scientific terminology.