High-Yield Chemistry: Bond Types, Molecular Geometry, and Polarity

Ionic

metal + nonmetal, electron transfer, ΔEN ≥ 2.0

Covalent

nonmetal + nonmetal, electron sharing

Metallic

sea of electrons, conductive, malleable

Lewis Symbols

8 valence electrons = stable; H only needs 2 electrons; Dots placed singly first → then paired

Lattice Energy

Lattice energy ↑ when: 1️⃣ Charges are larger; Q×Q matters MORE than size; CaO (2×2) > NaCl (1×1); 2️⃣ Ion size decreases; Smaller ions = stronger attraction; LiCl > NaCl > KCl > CsCl

Bond length

distance at minimum energy

Polarity rules

ΔEN = 0 → pure covalent; 0.1-0.4 → nonpolar covalent; 0.5-1.9 → polar covalent; ≥ 2.0 → ionic

Most polar bond

biggest ΔEN; F is the MOST electronegative (4.0)

Resonance

O₃, SO₂, NO₃⁻, CO₃²⁻ all have resonance; Bond order between single & double

Formal Charge

Formula: FC = valence - (lone electrons + ½ bonding); Best structure has: Formal charges closest to 0; Negative charge on most EN atom

Bond Energies

Breaking bonds: + (energy absorbed); Forming bonds: - (energy released); ΔHrxn = Σ(bonds broken) - Σ(bonds formed)

VSEPR BASIC RULES

Bond angle + shape depend on steric number (SN): SN = # bonded atoms + # lone pairs

Linear Shape

SN = 2, 0 lone pairs, angle = 180°

Trigonal planar Shape

SN = 3, 0 lone pairs, angle = 120°

Bent Shape

SN = 3, 1 lone pair, angle < 120°

Tetrahedral Shape

SN = 4, 0 lone pairs, angle = 109.5°

Trigonal pyramidal Shape

SN = 4, 1 lone pair, angle < 109.5°

Octahedral Shape

SN = 6, 0 lone pairs, angle = 90°

Sigma bonds

Every single bond = σ only

Double bond

1 σ + 1 π

Triple bond

1 σ + 2 π

Bond Rotation

σ bonds rotate freely; π bonds prevent rotation → cis/trans isomers