How do you find relative atomic mass?

1 Answer
Monzur R.
Oct 4, 2016

Find out the mean of all an atom's isotopic masses.

Explanation:

An atom's isotopic mass is the sum of its protons and neutrons - we'll exclude electrons because they've negligible weight. Then we work out the mean of its isotopes using their abundances.

For example, chlorine has two isotopes: #""^35"Cl"# at about #75%# abundance and #""^37"Cl"# at about #25%# abundance. Chlorine's relative atomic mass #= 35 * 0.75 + 37*0.25 = 35.5#

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