Question

Which of the following solids has a completely filled valence band and a large band gap?

• A. Conductor
• B. Semiconductor
• C. Insulator
• D. Superconductor

Hint:

Conductivity of semiconductors increases with temperature (as more electrons jump the gap), while the conductivity of metals (conductors) decreases with temperature due to increased lattice vibrations.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Solid materials are classified into conductors, semiconductors, and insulators based on their energy band structure, specifically the gap between the valence band and the conduction band.
Step 2: Detailed Explanation:
- Conductors: The valence and conduction bands overlap, or the valence band is partially filled. Electrons move freely.
- Semiconductors: There is a small energy gap (typically \(<3 \) eV) between a filled valence band and an empty conduction band. Thermal energy can excite some electrons across the gap.
- Insulators: The valence band is completely filled, and there is a very large energy gap (typically \(>3 \) to \( 5 \) eV) to the conduction band. Electrons cannot easily jump to the conduction band at room temperature, resulting in very low conductivity.
Step 3: Final Answer:
An insulator is characterized by a completely filled valence band and a large band gap.