noun
diatomic
Scientific term used in chemistry and physics to describe molecules consisting of two atoms.
酸素は二原子分子である。
Oxygen is a diatomic molecule.
多原子 means 'polyatomic' (many atoms), contrasting with the specific two-atom meaning of 二原子.
Compound of 二 (に, 'two') and 原子 (げんし, 'atom').