Question

Define london force.

Answer 1

London dispersion forces:

$\to$Weakest intermolecular forces

$\to$Temporary attractive forces that results when the electron in $2$ adjacent atoms occupy positions that make atoms form temporary dipoles.

$\to$Also know as induced dipole-induced dipole attraction or instantaneous dipole induced dipole forces.

$\to$These forces cause non-polar substances to condense to liquids and to freeze to solids, when temperature is lowered sufficiently.

$\to$Exist in molecules such as $F_2,O_2,N_2$ and even in mono-atomic molecules $He,Ne,Ar$ etc.

$\to$Electron of a neutral molecule keep on oscillating with respect to nuclei of atoms. As a result at an instant, positive charge may concentrate in one region and negative charge in another region in same molecule causing 'self-polarization' of molecule.

$\to$This polarized molecule may induce a dipole moment in a neighboring molecule

(Image 1)

$\to$Second atom can be distorted by appearance of dipole in first atom or molecule resulting to electrostatic attraction between $2$ atoms or molecule.

(Image 2)