Polarisability
The ease with which the electron cloud of an atom, ion or molecule can be distorted by an external electric field.
Formula / equation
μ_induced = α × E
Unit
C·m²/V
In depth
Polarisability increases with size and with the number of loosely held electrons, so large anions and heavy atoms are highly polarisable. It determines the strength of London dispersion forces, which is why boiling points climb down the halogen and noble gas groups.
Examples in the real world
I⁻ is far more polarisable than F⁻; iodine is a solid at room temperature while fluorine is a gas.