Chemistry: The Central Science (13th Edition)

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

Chapter 7 - Periodic Properties of the Elements - Exercises - Page 292: 7.43c

Answer

$K$ has smaller first ionization energy.

Work Step by Step

The periodic trend of the first ionization energy: - Going from left to right across a period, the first ionization energy increases (since effective nuclear charge increases and atomic radii decrease). - Going from up to down in a group, the first ionization energy decreases (since effective nuclear charge only increases slightly but atomic radii increase largely). $K$ and $Co$ both belong to the same fourth period. From left to right, $K$ appears first, then comes $Co$. Therefore, the first ionization energy would increase from $K$ to $Co$. So $K$ has smaller first ionization energy.
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