Q.Why ionic crystals are hard and brittle?

Step 1. Ionic crystals are hard because their constituent ions are held in fixed positions by strong, three-dimensional electrostatic (Coulombic) attraction -- only a strong external force can displace the ions from their lattice sites at all, which is exactly what 'hardness' means.

Step 2. But if a sufficiently strong shear force DOES manage to shift one plane of ions relative to the next (by roughly one ionic spacing), the ions that were originally attracting each other (cation next to anion) end up aligned with LIKE-charged ions instead (cation next to cation, anion next to anion).

Step 3. This sudden alignment of like charges produces strong electrostatic REPULSION exactly where there was attraction before, and the crystal planes fly apart rather than sliding smoothly -- so the crystal fractures/shatters instead of bending or deforming plastically. …

Explain hardness (fixed ions, strong attraction resists displacement) and brittleness (shear brings like charges together, causing repulsion-d …

• Explaining only the hardness half and forgetting to explain WHY the same bonding also causes brittleness (the like-charge-repulsion mechanism …