How easily an electron cloud is distorted by an electric field; it increases with atomic size.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Polarizability is the ease with which an atom's or molecule's electron cloud is distorted by an external electric field, including the field of a nearby ion. Electrons in large atoms and ions lie farther from the nucleus and are held less tightly, so those species are highly polarizable. Polarizability increases down a group and with the number of electrons in the outer shells, and it is reduced by a high positive charge that holds the cloud firmly. Polarizability determines the strength of London dispersion forces and contributes to the covalent character of ionic compounds. It is expressed as a volume.
Key ideas: Remember trends: polarizability rises down a group and to the left in a period, and anions are more polarizable than cations. Dispersion energy scales roughly with polarizability squared, divided by distance to the sixth power. So large, electron-rich molecules like I2 or long alkanes show strong dispersion attraction. Units are volume, such as cubic angstroms.
Common mistakes and connections: Students confuse polarizability with polarity: Xe is highly polarizable but nonpolar, and water is polar but not very polarizable. Another error is assuming the smaller the atom the more polarizable it is, which is reversed. Links to London forces, Fajans' rules, boiling points of noble gases and halogens.
Polarizability volume increases down the noble gas group as the larger electron clouds are easier to distort, which also strengthens dispersion forces. The interactive lesson shows this as a live animation or chart.
Iodine molecules are far more polarizable than fluorine molecules, which is why I2 has much stronger dispersion forces and a higher boiling point.
How easily an electron cloud is distorted by an electric field; it increases with atomic size.
Polarizability is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: Polar and Nonpolar Molecules, Percent Ionic Character, Fajans' Rules.
The next topics in Bonding & Molecular Structure are Lattice Energy and Born-Haber Cycle.
Yes. The interactive lesson includes a self-check question on Polarizability, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Polarizability is topic 26 of 104 in Bonding & Molecular Structure.