Chemistry · Ch 1 — Solid State
Insulators
Insulators
In an insulator, the valence band is completely filled with electrons while the conduction band above it is entirely empty, and the two bands are separated by a large energy gap called the forbidden zone (Fig. 1.24). Thermal energy is insufficient to promote electrons across this large gap from the valence band into the conduction band. As a result, the conduction band of an insulator remains permanently vacant, and with no mobile electrons available to carry a current, the material is an insulator. Most nonmetals and molecular solids show this large-band-gap behaviou …
Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your textbook's own diagram.
What this figure shows. A flat band diagram with three labelled parts: at the bottom a solid filled rectangle labelled 'Filled valence band'; at the top a tall empty rectangle labelled 'Empty conduction band'; and between them a vertical double-headed arrow with the two-line label 'Forbidden zone (Large energy gap)'. The gap is drawn conspicuously large -- thermal energy cannot promote electrons across it, …