Chemistry: The Central Science (13th Edition)

Published by Prentice Hall
ISBN 10: 0321910419
ISBN 13: 978-0-32191-041-7

Chapter 2 - Atoms, Molecules, and Ions - Exercises: 2.34b

Answer

This number is an average, not the mass of an individual isotope.

Work Step by Step

The atomic mass of carbon is written as 12.011 amu because this is the average mass of all carbon isotopes. Because the vast majority of carbon isotopes in the world are carbon-12, this number is extremely close to 12. However, because other carbon isotopes exist, this average is slightly above 12 amu.
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