Relative Atomic Mass (OCR GCSE Chemistry A (Gateway Science Suite)): Flashcards

Mass of one atom compared to 1/12th the mass of a carbon-12 atom

Abundance of each isotope

Weighted average of all isotopes

Ar is average; mass number is for one isotope

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

Chlorine-35 and Chlorine-37

75%

35.5

It's a weighted average of different isotopes

Periodic table

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

Relative formula mass (Mr)