If you're struggling to calculate the mass of chemical compounds, this video gives you a clear, step-by-step method. You'll learn what relative atomic mass and relative formula mass actually mean, where to find the values you need, and how to apply them to both simple molecules and ionic compounds with brackets. By the end you'll be able to calculate Mr for any compound — the essential first step in almost every quantitative chemistry calculation.

What You Will Learn

01:10What relative atomic mass (Ar) is and why it is defined relative to carbon-12.

02:48What relative formula mass (Mr) is and how it differs from Ar.

03:23How to calculate Mr for a simple molecular compound by summing the Ar values of each atom.

04:26How to handle brackets in formulae when calculating Mr, using the bracket multiplier correctly.

05:52How to calculate Mr for ionic compounds that contain polyatomic ions with brackets.

07:08Why the Mr of an ionic compound is still calculated from its empirical formula, not a structural formula.

08:38How isotopes affect the Ar values listed in the periodic table and why Ar is often not a whole number.

10:01How to use condensed structural formulae to identify the atoms present before calculating Mr.