Relative Atomic Mass - GCSE Chemistry Definition

Relative atomic mass is a way of comparing the mass of an atom of an element to one-twelfth of the mass of a carbon-12 atom, which is used as the standard reference.

Because most elements exist as a mixture of isotopes, relative atomic mass is a weighted average of the masses of all the isotopes of that element. This is why it is often not a whole number.

Understanding relative atomic mass is important in GCSE Chemistry for:

• Calculating masses in chemical reactions

• Working out molar masses and empirical formulas

For example, the relative atomic mass of chlorine is approximately 35.5, as it is an average of two main isotopes: Cl-35 and Cl-37.