1.23     Explain the following terms with suitable examples

                    (iv) F-centres

Answers (1)

When any negative ion is absent from lattice site then result the crystal now has an excess of cations. To maintain electrical neutrality the vacant anionic site is occupied by an electron as shown in the figure.

The anionic sites occupied by unpaired electrons are called F-centres. The F- centre is responsible for most interstitial properties of the compound.

This defect can be observed in  NaCl.