Polarity: definition in chemistry
Polarity: An uneven distribution of electric charge in a bond or molecule, giving one end a partial negative charge (δ−) and the other a partial positive charge (δ+).
A bond is polar when its two atoms differ in electronegativity, so the shared electrons are pulled closer to one of them. A molecule is polar only if its polar bonds do not cancel out because of its shape: carbon dioxide has polar bonds but is linear and nonpolar overall, while bent water is polar. Polarity affects boiling points, solubility and how molecules attract one another, as summed up by the rule that like dissolves like.
Examples
- Water (H₂O) — polar, with δ− on the oxygen
- Hydrogen chloride (HCl) — polar, with δ− on the chlorine
- Carbon dioxide (CO₂) — polar bonds, but a nonpolar molecule
- Oil and water do not mix because oil is nonpolar
On the periodic table
The bigger the difference in electronegativity between two elements, which rises toward the upper right of the table, the more polar the bond between them, as in H–F and O–H.