A convenient amount unit for expressing very large numbers of atoms or molecules is the mole. Formulas or formulae -le 1. The word symmetry implies balance.
Molecules are distinguished from ions by their lack of electrical charge.
The formula mass of a substance is the sum of the average atomic masses of each atom represented in the chemical formula and is expressed in atomic mass units. Structural isomers are isomers that have the same component atoms but they are arranged differently from each other. Learn more about isomerism in this article. Structural isomerism is also known as constitutional isomerism.