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: 2.88a


2 protons, 2 electrons, 1 neutron

Work Step by Step

Helium has an atomic number of 2 (it is number 2 on the periodic table), therefore it has 2 protons. The mass number given on 3He is 3, which is the number of protons + neutrons. Therefore, if it has 2 protons then 3-2 = 1 neutron. Finally, it is not charged so the positive charges (protons) must balance the negative charges (electrons). Thus, we have 2 electrons.
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