nonpolar

Meaning: A bond is nonpolar when the two atoms have equal or nearly equal electronegativity, so electrons are shared about equally (H–H, Cl–Cl; C–H is treated as nonpolar). A molecule is nonpolar when its net dipole is zero, either because every bond is nonpolar or because polar bond dipoles cancel by symmetry (CO₂, CCl₄). Nonpolar molecules attract one another through London dispersion forces, which strengthen with size and surface area.

Equation: μ = q × d, where μ is the bond dipole moment (C·m), q is the separated partial charge (C), and d is the distance between the charges (m). A molecule's net dipole is the vector sum of its bond dipoles. Nonpolar means that sum is zero.

On the MCAT: Expect questions on solubility (like dissolves like), relative boiling points, and which solvent extracts a compound. In normal-phase chromatography on polar silica, nonpolar compounds elute first. Nonpolar amino acid side chains tend to sit in protein interiors, and lipid tails form the membrane core.

Common confusion: Polar bonds do not guarantee a polar molecule. CO₂ has polar C=O bonds but is linear and nonpolar. Check the geometry. Lone pairs or unlike substituents (H₂O, CHCl₃) leave a net dipole, so those molecules are polar.