Question

How would you decide that a given hard and rigid solid possessing high melting and boiling points is ionic or covalent?

Answer 1

1. Electrical Conductivity: Ionic solids conduct electricity in molten or aqueous states, but not in the solid state. Covalent solids do not conduct electricity in any state (except graphite).
2. Solubility: Ionic solids are generally soluble in polar solvents like water but insoluble in non-polar solvents. Covalent solids are usually insoluble in polar solvents but soluble in non-polar solvents.
3. Fracture Behaviour: Ionic solids are brittle and tend to cleave along specific planes when struck. Covalent solids are usually hard and not brittle, with the exception of some like diamond.
4. Lattice Structure: Ionic solids form a 3D ionic lattice with alternating positive and negative ions. Covalent solids have a network of covalent bonds forming a giant molecular structure.
5. Examples:
   1. Ionic solid: NaCl, KBr, CaF₂, etc.
   2. Covalent solid: Diamond, quartz (SiO₂), silicon carbide (SiC), etc.