Molecules with net dipole moment are polar; symmetrical ones with canceling dipoles are nonpolar.
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A molecule is polar when it has a net dipole moment, which requires both polar bonds and an asymmetric shape so that the bond dipoles do not cancel. Symmetric molecules such as carbon dioxide, boron trifluoride and methane are nonpolar even though their individual bonds are polar. Polar molecules dissolve well in polar solvents such as water and tend to align with an applied electric field. Nonpolar molecules mix more readily with nonpolar solvents, following the principle that like dissolves like. The distinction governs solubility, boiling point and many reaction pathways.
Key ideas: Use the two-step test: first find polar bonds, then draw the shape and check whether the dipoles cancel. Symmetric shapes with identical terminal atoms cancel: linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral and square planar. Lone pairs on the central atom usually make the molecule polar, except for symmetric cases such as XeF4 and XeF2.
Common mistakes and connections: A classic mistake is judging by bonds alone, which makes CO2 and CCl4 look polar. Another is forgetting that replacing one substituent breaks symmetry: CH3Cl is polar, but CH4 is not. Cis-1,2-dichloroethene is polar while the trans isomer is not. Links to VSEPR, solubility, boiling points and chromatography.
Each C=O bond is polar, but the two dipoles point in opposite directions along a straight line and cancel, so CO2 is nonpolar overall. The interactive lesson shows this as a live animation or chart.
Chloroform, CHCl3, is polar, whereas carbon tetrachloride, CCl4, is nonpolar because its four C-Cl dipoles cancel.
Molecules with net dipole moment are polar; symmetrical ones with canceling dipoles are nonpolar.
Polar and Nonpolar Molecules is a beginner topic in Bonding & Molecular Structure. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Bonding & Molecular Structure first: Bond Order, Bond Polarity, Dipole Moment.
The next topics in Bonding & Molecular Structure are Percent Ionic Character and Fajans' Rules.
Yes. The interactive lesson includes a self-check question on Polar and Nonpolar Molecules, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Polar and Nonpolar Molecules is topic 23 of 104 in Bonding & Molecular Structure.