University Physics with Modern Physics (14th Edition)

Published by Pearson
ISBN 10: 0321973615
ISBN 13: 978-0-32197-361-0

Chapter 42 - Molecules and Condensed Matter - Problems - Discussion Questions - Page 1434: Q42.12


The structure of the energy bands determines opacity.

Work Step by Step

In an ionic crystal, which is insulating because electrons are immobile, the energy gap is large. There are no easily accessible energy states for electrons in the filled valance band to go if they were to absorb a visible photon, so the photon passes through unimpeded. In contrast, in a metal, the conduction band is already partially filled, and electrons can absorb photons, making the material opaque.
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