Atomicity
The number of atoms present in one molecule of an element.
Unit
Dimensionless
In depth
Atomicity classifies elemental molecules as monatomic, diatomic, triatomic or polyatomic. It reflects how strongly the element's atoms bond to themselves: noble gases with filled shells stay monatomic, while sulfur and phosphorus form large rings and cages that maximise the number of covalent bonds.
Examples in the real world
He is monatomic, O₂ diatomic, O₃ triatomic, P₄ tetratomic and S₈ octatomic.