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

Explanation

(a) Basis of similarities
(i) Both ionic and metallic crystals have electrostatic forces of attraction. In ionic crystals, these are between the oppositely charged ions while in metals, these are among the valence electrons are free to move and hence they conduct electricity in the solid state.
(ii) Ionic bond in ionic crystals in strong due to electrostatic forces of attraction. However, metallic bond may be weak or strong depending upon the number of valence electrons and the size of the kernels.
(b) Ionic crystals are hard because there are strong electrostatic forces of attraction among the oppositely charged ions. They are brittle because the ionic bond is non-directional .