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 - Additional Exercises - Page 78: 2.93a


$^{6}$Li: 3 protons and 3 neutrons $^{7}$Li: 3 protons and 4 neutrons

Work Step by Step

Lithium always has 3 protons, regardless of the isotope. That means that the rest of the atomic mass must be from the neutrons. For $^{6}$Li, it has an atomic mass of 6. $6-3=3$ , so there must be 3 neutrons. For $^{7}$Li it has an atomic mass of 7. $7-3=4$, so there must be 4 neutrons.
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