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: 2.27f

Answer

Protons: 95 Neutrons: 148 Electrons: 95

Work Step by Step

The problem gives the atomic mass number of the isotope, 243, and shows that the element given is Americium (as indicated by the symbol Am). First of all, the atomic number of Americium, as the periodic table shows, is 95. This means that all Americium isotopes have 95 protons. Next, the atomic mass number states that the atomic mass of this isotope is 243 amu. Because both protons and neutrons weigh one amu while electrons are essentially weightless, this means that there must be 148 neutrons (95 protons+148 neutrons= 243 amu). Finally, the symbol does not indicate a charge on the isotope, meaning that this isotope is neutral. Thus, the number of protons and the number of electrons must be equal, as protons have a +1 charge, electrons have a -1 charge, and neutrons have no charge at all.
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