Question

In the boron atom, the single $\mathbf{2}\mathbf{p}$ electron does not completely fill any $\mathbf{2}\mathbf{p}$ spatial state, yet solid boron is not a conductor. What might explain this? (It may be helpful to consider again why beryllium is not an insulator.)

Short answer

Overlapping the two electrons and one makes a boron an Insulator.

Step-by-step solution

A concept:

Boron is a chemical element with symbol B and atomic number $\mathbf{5}$ . Boron is classified as a metalloid, it is a solid at room temperature.

Step-2: Reason for boron an insulator:

In the boron atom, the $2\mathrm{s}$ band and $2\mathrm{p}$ band overlap. Without overlapping, the $2\mathrm{s}$ band should be filled with the two$2\mathrm{s}$ electrons and the $2\mathrm{p}$ band should be partially filled with the one $2\mathrm{p}$ electron. That would make Boron a conductor. However, with overlapping, the two $2\mathrm{s}$ electrons and one $2\mathrm{p}$ electron will fill up the combined overlapping $2\mathrm{s}$ and $2\mathrm{p}$ band, making boron an insulator..