Why Do Atoms Bond?
Atoms bond to achieve a full outer electron shell — the stable configuration of a noble gas (8 electrons in the outer shell, or 2 for the innermost shell). This is the octet rule.
Ionic Bonding
Ionic bonds form between metals and non-metals. The metal loses electrons (becomes a positive ion — cation) and the non-metal gains electrons (becomes a negative ion — anion). The opposite charges attract.
Example: Sodium Chloride (NaCl)
Na (2,8,1) → loses 1 electron → Na⁺ (2,8)
Cl (2,8,7) → gains 1 electron → Cl⁻ (2,8,8)
Na⁺ and Cl⁻ attract each other → ionic bond formed.
Properties of Ionic Compounds
- High melting and boiling points (strong electrostatic forces)
- Conduct electricity when dissolved in water or melted (ions are free to move)
- Crystalline solid at room temperature
Covalent Bonding
Covalent bonds form between non-metals. Atoms share pairs of electrons.
Example: Water (H₂O)
Oxygen needs 2 more electrons; each hydrogen needs 1 more.
Each O–H bond is a shared pair of electrons.
Types of Covalent Bonds
- Single bond: one shared pair — H–H (H₂)
- Double bond: two shared pairs — O=O (O₂)
- Triple bond: three shared pairs — N≡N (N₂)
💡 Ionic compounds tend to dissolve in water; many covalent compounds do not. This is why salt dissolves in water but oil does not.