non-polar
Summary
Non-polar describes a bond or molecule with no net charge separation, because electrons are shared about equally or polar bond dipoles cancel by symmetry. Most testable: non-polar substances dissolve best in non-polar solvents (like dissolves like) and attract each other mainly through London dispersion forces.
Detail
Meaning: A bond is non-polar when two atoms share electrons equally or nearly so, as in H₂, Cl₂, C–C and C–H (electronegativity difference about 0.4). A molecule is non-polar when it has no net dipole: either all its bonds are non-polar (hydrocarbons) or its polar bonds are arranged symmetrically so the dipoles cancel (CO₂, CCl₄, BF₃). Non-polar molecules attract one another mainly by London dispersion forces, so they are hydrophobic and usually boil lower than polar molecules of similar size.
On the MCAT: Expect "like dissolves like" solubility questions, boiling-point rankings, and extractions in which non-polar compounds go to the organic layer rather than the water layer. In normal-phase chromatography on polar silica, non-polar compounds elute first. In biology passages, lipid tails and non-polar side chains cluster away from water in membranes and protein cores.
Common confusion: Polar bonds do not guarantee a polar molecule. CO₂ has two polar C=O bonds but is non-polar because they point in opposite directions. Molecular geometry from VSEPR decides, which is why bent H₂O is polar while linear CO₂ is not.
Sources
- Organic Chemistry by Paula Bruice
- Organic Chemistry by John McMurry
- Organic Chemistry by David Klein
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.