Chemical Bonding
Chemical bonding is the force of attraction that holds atoms together. Atoms bond to achieve a stable electron configuration — typically a full outer shell of 8 electrons (the octet rule).
A. Types of Chemical Bonds — Overview
Four Bond Types at a Glance
| Bond Type | How It Forms | Typical Properties | Examples |
|---|---|---|---|
| Ionic | Transfer of electrons from metal to non-metal. Metal loses e⁻ (→ cation), non-metal gains e⁻ (→ anion). | High melting point, conducts electricity when dissolved/molten, brittle, crystalline | NaCl, MgO, KBr, CaCl₂ |
| Covalent | Sharing of electrons between two non-metals. Each atom contributes electrons to shared pair(s). | Low melting point, poor conductor (usually), can be solid/liquid/gas at room temp | H₂O, CO₂, CH₄, HCl, NH₃ |
| Metallic | Metal cations in a "sea" of delocalized electrons. Electrons move freely through the metal lattice. | Conducts electricity and heat, malleable, ductile, lustrous (shiny) | Fe, Cu, Al, Na, Mg, Au |
| Hydrogen Bond | Weak attraction between a δ+ hydrogen and a lone pair on a highly electronegative atom (F, O, N). | Much weaker than the above — responsible for water's unusually high boiling point | H₂O (between molecules), DNA base pairs, proteins |
Ionic
How It FormsTransfer of electrons from metal to non-metal. Metal loses e⁻ (→ cation), non-metal gains e⁻ (→ anion).
Typical PropertiesHigh melting point, conducts electricity when dissolved/molten, brittle, crystalline
ExamplesNaCl, MgO, KBr, CaCl₂
Covalent
How It FormsSharing of electrons between two non-metals. Each atom contributes electrons to shared pair(s).
Typical PropertiesLow melting point, poor conductor (usually), can be solid/liquid/gas at room temp
ExamplesH₂O, CO₂, CH₄, HCl, NH₃
Metallic
How It FormsMetal cations in a "sea" of delocalized electrons. Electrons move freely through the metal lattice.
Typical PropertiesConducts electricity and heat, malleable, ductile, lustrous (shiny)
ExamplesFe, Cu, Al, Na, Mg, Au
Hydrogen Bond
How It FormsWeak attraction between a δ+ hydrogen and a lone pair on a highly electronegative atom (F, O, N).
Typical PropertiesMuch weaker than the above — responsible for water's unusually high boiling point
ExamplesH₂O (between molecules), DNA base pairs, proteins
⚡ MCQ Tip Ionic = metal + non-metal (electron transfer). Covalent = non-metal + non-metal (sharing). Metallic = metal + metal. Hydrogen bond is the WEAKEST of the four. Ionic compounds conduct electricity only when dissolved or molten.
B. Ionic Bonding in Detail
Electron Transfer — NaCl Example
- Na (2,8,1) loses its 1 valence electron → Na⁺ (2,8) — achieves stable octet
- Cl (2,8,7) gains 1 electron → Cl⁻ (2,8,8) — achieves stable octet
- Oppositely charged ions attract each other — forming a giant ionic lattice
General Rule
Metal loses e⁻ → Cation (+) | Non-metal gains e⁻ → Anion (−)
| Property | Explanation |
|---|---|
| High melting point | Strong electrostatic attraction between oppositely charged ions needs much energy to overcome |
| Conducts when dissolved/molten | Ions become free to move and carry charge — but NOT as solid (ions fixed in lattice) |
| Brittle | Shifting layers brings like charges together → repulsion → shatters |
| Soluble in water (usually) | Polar water molecules pull ions apart from the lattice |
C. Covalent Bonding in Detail
Single, Double & Triple Bonds
| Bond Order | Shared Pairs | Example | Bond Strength |
|---|---|---|---|
| Single bond | 1 pair (2 electrons) | H–H (H₂), H–Cl (HCl) | Weakest covalent |
| Double bond | 2 pairs (4 electrons) | O=O (O₂), C=O (CO₂) | Stronger, shorter |
| Triple bond | 3 pairs (6 electrons) | N≡N (N₂) | Strongest, shortest |
D. Metallic Bonding
Sea of Electrons Model
- Metal atoms release their valence electrons into a shared "sea" of delocalized electrons
- Positive metal ions (cations) are held together by attraction to this mobile electron sea
- Conducts electricity: delocalized electrons move freely to carry charge
- Conducts heat: electrons transfer kinetic energy rapidly
- Malleable & ductile: layers of ions can slide without breaking — electrons maintain attraction throughout
- Lustrous: free electrons reflect light
E. Polar vs Non-polar Covalent Bonds
Electronegativity & Bond Polarity
| Type | Electron Sharing | Electronegativity | Examples |
|---|---|---|---|
| Non-polar Covalent | Electrons shared equally — symmetrical distribution | Same (or very similar) — ΔEN ≈ 0 | H₂, O₂, N₂, Cl₂, F₂, Br₂, I₂ |
| Polar Covalent | Electrons pulled closer to more electronegative atom — δ+ and δ− ends | Different — ΔEN > 0 | H₂O, HCl, NH₃, HF, SO₂ |
Non-polar Covalent
Electron SharingElectrons shared equally — symmetrical distribution
ElectronegativitySame (or very similar) — ΔEN ≈ 0
ExamplesH₂, O₂, N₂, Cl₂, F₂, Br₂, I₂
Polar Covalent
Electron SharingElectrons pulled closer to more electronegative atom — δ+ and δ− ends
ElectronegativityDifferent — ΔEN > 0
ExamplesH₂O, HCl, NH₃, HF, SO₂
⚡ Electronegativity order (high → low): F > O > N > Cl > Br > C > H. Water (H₂O) is polar covalent — oxygen is more electronegative, pulling electrons towards itself (δ−), leaving H as δ+.
Quick MCQ Revision
| Fact | Answer |
|---|---|
| Ionic bond forms between | Metal + Non-metal (electron transfer) |
| Covalent bond forms between | Non-metal + Non-metal (electron sharing) |
| Metallic bond features | Sea of delocalized electrons — conducts, malleable, ductile |
| Weakest bond type | Hydrogen bond |
| NaCl bond type | Ionic (Na loses 1e⁻ → Na⁺; Cl gains 1e⁻ → Cl⁻) |
| H₂O bond type | Polar covalent (O more electronegative) |
| H₂ bond type | Non-polar covalent (same electronegativity) |
| Ionic compounds conduct when | Dissolved in water OR molten (not solid) |
| Octet rule | Atoms bond to achieve 8 electrons in outer shell |