Chemical Bonding

Chemical Bond: The force of attraction that holds atoms together in a molecule. Octet Rule: Atoms tend to gain, lose, or share electrons to attain 8 electrons in their valence shell (noble gas configuration).

Determines molecular geometry based on repulsion between electron pairs. Order of Repulsion: Lone Pair-Lone Pair > Lone Pair-Bond Pair > Bond Pair-Bond Pair.

• AB₂ (Linear): 180° angle. e.g., BeCl₂.
• AB₃ (Trigonal Planar): 120° angle. e.g., BF₃.
• AB₄ (Tetrahedral): 109.5° angle. e.g., CH₄.
• Effect of Lone Pairs:
  • NH₃: 1 Lone Pair, Trigonal Pyramidal, 107.5°.
  • H₂O: 2 Lone Pairs, Bent/Angular, 104.5°.

Sigma (σ) Linkage: Formed by head-to-head overlap (s-s, s-p, p-p). Stronger bond.

Pi (π) Linkage: Formed by sideways/parallel overlap (p-p). Weaker bond, electron density above and below the axis.

Mixing of atomic orbitals to form equivalent hybrid orbitals.

• sp³ Hybridization: 1s + 3p → 4 sp³ orbitals. Tetrahedral (109.5°). e.g., CH₄, C₂H₆.
• sp² Hybridization: 1s + 2p → 3 sp² orbitals. Trigonal Planar (120°). One unhybridized p-orbital forms π-bond. e.g., Ethene (C₂H₄).
• sp Hybridization: 1s + 1p → 2 sp orbitals. Linear (180°). Two unhybridized p-orbitals form 2 π-bonds. e.g., Ethyne (C₂H₂).

Electrons reside in molecular orbitals (Atomic Orbitals → Bonding MO + Antibonding MO). Bond Order (B.O.): (N_b - N_a) / 2.

Paramagnetism: O₂ is paramagnetic because it has 2 unpaired electrons in antibonding π* orbitals.

Dipole-Dipole Forces: Between polar molecules (e.g., HCl).

Hydrogen Bonding: Strong force between H connected to N, O, F and a lone pair on another electronegative atom. Anomalous properties of water (high b.p.) due to H-bonding.

London Dispersion Forces: Instantaneous dipole-induced dipole forces. Significant in non-polar molecules and noble gases.