orbital hybridization

Meaning: Orbital hybridization is a valence bond model in which s and p orbitals on one atom mix into equivalent hybrid orbitals aimed at its electron domains (bonded atoms plus lone pairs). Two domains give sp (linear, 180°), three give sp² (trigonal planar, 120°), four give sp³ (tetrahedral, about 109.5°). Hybrids form σ bonds and hold lone pairs; leftover unhybridized p orbitals form π bonds.

Equation: hybrid orbitals formed = atomic orbitals mixed = electron domains on the atom (a unitless count). Example: one s + three p → four sp³ orbitals.

On the MCAT: You may be asked to assign hybridization from a structure, give the geometry or bond angles, or count σ and π bonds (double bond = 1 σ + 1 π; triple bond = 1 σ + 2 π). Another favorite is s character: sp is 50%, sp² is 33%, sp³ is 25%. More s character gives shorter, stronger bonds and a more acidic C–H, so acidity runs alkyne > alkene > alkane.

Common confusion: Count domains, not bonds. A double bond is one domain, so the carbon in C=O is sp². Lone pairs count as domains too, so the O in water is sp³ (bent), not sp².