molecule

The smallest particle of a specific element or compound that retains the chemical properties of that element or compound; two or more atoms held together by chemical bonds.

Hydrogen chloride is a diatomic molecule, consisting of a hydrogen atom and a chlorine atom.

The critical component of the photosynthetic system is the “water-oxidizing complex”, made up of manganese atoms and a calcium atom. This system splits water molecules and delivers some of their electrons to other molecules that help build up carbohydrates.

A tiny amount.