- the smallest physical unit of an element or compound, consisting of one or more like atoms in an element and two or more different atoms in a compound.
- a quantity of a substance, the weight of which, measured in any chosen unit, is numerically equal to the molecular weight; gram molecule.
- any very small particle.
- the simplest unit of a chemical compound that can exist, consisting of two or more atoms held together by chemical bonds
- a very small particle
