Cornell Note: Hybridization Deep Dive

Cue Column | Notes Column

Cue	Notes
sp3 hybridization	1s + 3p → 4 equivalent orbitals. Tetrahedral (109.5°). 25% s-character. Examples: CH4 (SMILES: `C`), C2H6 (`CC`), all saturated C
sp2 hybridization	1s + 2p → 3 equivalent orbitals in one plane. Trigonal planar (120°). 33.3% s-character. One unhybridized p-orbital forms pi bond. Examples: C2H4 (`C=C`), aldehydes, ketones, carbocations
sp hybridization	1s + 1p → 2 equivalent orbitals (linear, 180°). 50% s-character. Two unhybridized p-orbitals form two pi bonds. Examples: C2H2 (`C#C`), CO2 (`O=C=O`), nitriles (`CC#N`)
% s-character formula	% s = $\frac{number of s orbitals}{total orbitals used}$ × 100
Bond length order	sp3 C-C (1.54 Å) > sp2 C-C (1.34 Å) > sp C-C (1.20 Å)
Bond strength order	sp C-H $\frac{558 kJ}{mol}$ > sp2 C-H $\frac{444 kJ}{mol}$ > sp3 C-H $\frac{410 kJ}{mol}$
Electronegativity of C	sp (3.1) > sp2 (2.75) > sp3 (2.48) on Pauling scale
NEET trap	CO2 is sp hybridized (not sp2) — two double bonds = two sigma + two pi
NEET trap	Carbocation carbon is sp2 (empty p-orbital, not sp3)

Summary:

The three hybridizations are directly connected to molecular geometry, bond properties, and acidity. The key NEET discriminator is recognizing sp in unusual cases like CO2, CS2, and nitrile group.