Question

Explain why ionic solids are hard and brittle?

Answer 1

Hint:
There is a presence of strong electrostatic forces of attraction in ionic solids which makes the ionic solids hard and there is also a non – directional nature in ionic crystals therefore, ionic bonds are brittle.

Complete step by step answer:
Ionic solids are those solids which are composed of oppositely charged ions arranged in such a way that there is alternative space with uneven atomic size and there also exists electrostatic force of attraction in between these ions which makes them electrically inert in their solid state. Ionic solids have high melting points than metallic but have less melting point than covalent.
-There are some characteristics of ionic solids:
-The ionic solids do not conduct electricity when they are in solid state.
-They have low volatility with high melting and boiling points.
-The solubility in polar and non – polar solvents depends upon the presence of electrostatic force of attraction which exists in between the cations and anions.
-The ionic solids are insoluble in non – polar solvents due to the presence of low dielectric constant values.
-Ionic solids can be soluble in polar solvents like water as it has dipole so the positive end of dipole interacts with negative ions of ionic solids while negative end of dipole interacts with positive ions of the same ionic crystals.
-The ionic solids are hard and brittle because the ions in ionic solids are held in a lattice due to the electrostatic forces of attraction in cations and anions as well as the repulsion with the like charges. If a large enough force is applied along a certain plane this causes ions to shift along that layer which displaces that layer with respect to the next so, there will be the repulsion between like charges with ionic compounds. Because the ionic solids are localized, these solids tend to be stiff and brittle like covalent solids.

Note:
The ionic solids are never found in gaseous or liquid state under normal conditions of temperature and pressure because ions lack mobility due to presence of electrostatic force in between oppositely charged ions. This lack of mobility of electrons makes ionic compounds never exist in gas or liquid states.