Why will you never find an atom that has an actual atomic mass equal to the elements average atomic mass?

Question

Robert Mills

Chemistry

14 April, 22:58

Why will you never find an atom that has an actual atomic mass equal to the elements average atomic mass?

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Gavyn Kaufman · Answer 1

Most all elements you see on the periodic table up to element 92 (uranium) are naturally occurring, and have at least two isotopes - atoms of the same element which contain the same number of protons, but a different number of neutrons.

Both protons and neutrons have an atomic mass of 1 "atomic mass unit" (amu). An atom containing 6 protons (carbon) can have 6, 7, or 8 neutrons. Respectively, they would have atomic masses of 12, 13, and 14 amu.

Over 99% of the carbon atoms found in nature have 6 neutrons (Carbon-12), a very small fraction have 8 neutrons (Carbon-14), and an even tinier fraction have 7 neutrons (Carbon-12). Taken as an average, the mass is 12.011 amu ... just a bit over 12 amu.