Question

In which type of metals, there is overlapping of valence band with the conduction band?

• A. Monovalent metals
• B. Divalent metals
• C. Trivalent metals
• D. Tetravalent metals

Hint:

Remember that the simple picture of filled bands suggesting insulating behavior is often corrected by band overlap. The primary example for this phenomenon is divalent metals, which would be insulators without this overlap.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
According to the band theory of solids, the electrical properties of a material are determined by the energy gap between its valence band and conduction band. For a material to be a good conductor (a metal), it must have electrons in the conduction band.
Step 2: Detailed Explanation:


Monovalent metals (like Sodium): The highest occupied band (the valence band) is only half-full. This partially filled band also acts as the conduction band, so electrons can easily move to empty energy states, making the material a conductor. An overlap is not necessary.
Divalent metals (like Magnesium, Beryllium, Zinc): These metals have two valence electrons. According to a simple model, their valence band should be completely full. If there were an energy gap between the full valence band and the next empty band (the conduction band), they would be insulators. However, divalent metals are good conductors. This is explained by the fact that the top of the filled valence band overlaps in energy with the bottom of the empty conduction band. This overlap provides empty energy states for electrons to move into, allowing for electrical conduction.
Trivalent and Tetravalent metals (like Aluminum): These metals have partially filled valence bands, which also act as conduction bands, making them conductive without the necessity of an overlap.

Step 3: Final Answer:
The classic case where band overlap is essential to explain metallic conductivity is for divalent metals.