Conditions for ionic bond formation

1. Large electronegativity difference (>1.7 Pauling units)
2. Low ionisation energy of the metal (easy electron loss)
3. High electron affinity of the non-metal (eager electron gain)
4. High lattice energy of the product (stabilises the ionic crystal)
5. Both ions achieve noble gas / stable configuration (octet rule)

Class 10 example — NaCl:

Na (2,8,1) → Na⁺ (2,8) + e⁻ [loses 1 electron]
Cl (2,8,7) + e⁻ → Cl⁻ (2,8,8) [gains 1 electron]
Na⁺ + Cl⁻ → NaCl (ionic bond via electrostatic attraction)