Lewis Dot, Chemical Bonds, Electronegativity, Resonance Structures

key points and trends

Bond Types

Ionic: metal + nonmetal (electrons transferred)
Covalent: nonmetal + nonmetal (electrons shared)
Polar Covalent: EN difference 0.5–1.7
Nonpolar Covalent: EN difference 0–0.4

Lewis Structure Rules

H and F are always terminal
Central atom = least electronegative (except H)
Fill outer atoms first, then central
If central lacks 8 → add double/triple bonds

Typical Bonding Patterns

H = 1 bond, 0 lone pairs
C = 4 bonds, 0 lone pairs
N = 3 bonds, 1 lone pair
O = 2 bonds, 2 lone pairs
Halogens = 1 bond, 3 lone pairs

Bond Order & Strength

Single = longest & weakest
Triple = shortest & strongest
Higher bond order → shorter & stronger

Formal Charge

FC = Valence – Nonbonding – (Bonding ÷ 2)
Best structure = smallest charges
Negative charge prefers more electronegative atoms

Resonance

Draw multiple structures if e⁻ can move
Real molecule = average
Resonance creates fractional bond order (ex: 1.5)

Octet Rule Exceptions

Electron Deficient (<8): BF₃, BeCl₂
Odd Electrons: NO, NO₂
Expanded Octet (>8): P, S, Cl, Xe, Br, I (Period 3+)

Electronegativity Trend

Increases ↑ and → across periodic table
F is highest EN

Bond Polarity by EN Difference

0–0.4 → Nonpolar
0.5–1.7 → Polar Covalent
>1.7 → Ionic

Lattice Energy Trend

Higher ion charge = MUCH stronger lattice energy
Smaller ions = stronger lattice energy (but charge matters more)

Bond Energy

Breaking bonds = endothermic
Forming bonds = exothermic