How can you find the number of neutrons in an atomic isotope? What is the difference between mass number and atomic mass?

1 Answer
Truong-Son N.
Sep 28, 2015

EX:

When you say "carbon-13", you are giving its mass number, #13#. Carbon is atomic number #6#. Add the number of neutrons and protons in the particular isotope you are looking at, and you get the mass number.

Therefore, "carbon-13" must have #overbrace(13)^"mass number" - overbrace(6)^"atomic number" = 7# neutrons.

Sidenote: #""^13 C# is the same as #""_6^13 C#.

The top number is the mass number, and the bottom number is the atomic number.

NOTE: The mass number is NOT the atomic mass. The atomic mass is the average mass number of all isotopes in existence. The mass number is for one isotope only.

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