Explain
a. The basic of sumilarities and differences between metallic and ionic crystals.
b. Ionic solids are hard and brittle.

Explanation

(a) Similarities . (i) Both ionic and metallic crystals have electrostatic forces forces of attraction. In ionic crystals theseare between the oppositely charged ions. In metals, these are among the valence electrons and the kernels. That is why both have high melting point.
(ii) In both cases, the bond is non-directional.
Difference . (i) In ionic crystals , the ions are not free to move. Hence,they cannot conduct electricity teh soild state. They can do so only in the molten state or in aqueous solution. In metals, the valence electrons are free to flow. Hence, they can conduct electricity in the solid state.
(ii) Ionic bond is strong due to electrostatic forces of attraction. Metallic bond may be weak or strong depending upon the number of valence electrons and the size of the kernels.
(b) Ionic crystals arte hard because there are strong electrostatic forces of attraction among the oppositely charged ions. they are brittle because ionic bond is non-directional.