Campbell Biology (11th Edition)

Published by Pearson
ISBN 10: 0-13409-341-0
ISBN 13: 978-0-13409-341-3

Chapter 2 - 2.2 - Concept Check - Page 36: 2



Work Step by Step

The top number is the mass number, equal to $\textrm{number of neutrons + protons}$. In the case of the radioactive nitrogen isotope, there are $8$ neutrons instead of $7$. The number of protons doesn't change, since we're dealing with nitrogen and nitrogen is defined as being the element with $7$ protons. Thus, the mass number is $7+8=15$. The bottom number is the atomic number, which is equal to the number of protons. We've already determined this to be $7$. The symbol for the element nitrogen is $\textrm{N}$.
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