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 types of crystals have electronstatic force of attraction. In ionic solids, these are between oppositely charged ions, whereas in metals, these are between kernels and valence electrons.
(ii) In both cases, the bond is non-directional.
Differences
(i) In ionic crystals, ion are not free to move. Hence, they cannot conduct electricity in solid state, but conduct electricity in fused (molten) or in aqueous solutions. In metals, the valence (or mobile) electrons are free to flow, hence they conduct electricity in the solid states.
Ionic bond is strong due to electrostatic force of attarction. Metallic bond may be weak or strong depending upon the number of mobile electrons and the size of the kernels (positive fixed part).
b. Ionic solids are hard because there are strong electrostatic force of attraction between the oppositely charged ions. They are britte because inoic bond is non-directional.