How can an atomic mass not be a whole number?

1 Answer
Ryuu
Nov 27, 2016

It's an average of all isotopes.

Explanation:

There are different isotopes of every element and the atomic mass is an average mass of all those isotopes.

E.g. Iron has for naturally occurring isotopes with masses: 53.940 #mu#, 55.935 #mu#, 56.935 #mu#, and 57.933 #mu#. If you get their abundances and multiply the corresponding mass to their abundance, you get the average atomic mass, which is 55.846 #mu#.

Hope this helps :)

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