Relative atomic mass (Edexcel GCSE Chemistry): Flashcards

1/12th the mass of a carbon-12 atom

Abundance of each isotope

Weighted average of all isotopes

Mass number = one isotope; Ar = weighted average

$\text{Ar} = \frac{\sum(\text{mass} \times \text{abundance})}{\text{total abundance}}$

75%

25%

35.5

Different isotopes contribute to weighted average

On the periodic table

$\text{Moles} = \frac{\text{Mass}}{\text{Ar or Mr}}$

Relative formula mass (Mr)