Answer
See answers.
Work Step by Step
Refer to the periodic table.
In sodium, the partially filled shell is the 3s shell. It has a capacity for 2 electrons, but only has one.
In chlorine, the partially filled shell is the 3p shell. It has a capacity for 6 electrons, but only has five.
When NaCl forms, the lone electron from sodium’s 3s shell moves to chlorine’s 3p shell. Now, both ions have filled outer shells.
See Figure 29-25b. When we consider the material as a whole, where the energy levels become bands, the resulting bands are either completely filled (“valence band”) or completely empty (“conduction band”). The large band gap means that few electrons can jump from the valence band to the conduction band. When a voltage is applied, the electrons find no accessible states, and there is no current.
With so few mobile electrons, NaCl is an insulator.
