Question

Define all these terms:
A.Dispersion Forces (or) London forces
B.Dipole – Dipole Forces
C.Dipole – induced Dipole forces

Answer 1

London or dispersion forces are a type of force that acts between atoms and molecules. Dipole – dipole forces are the type of intermolecular attraction between two molecules. A dipole - induced dipole force is a weak force that results when a polar molecule induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangement of electron clouds of the non-polar species.

Complete step by step answer:
A.Dispersion Forces (or) London forces:
London dispersion forces are a type of force that acts between atoms and molecules. These forces are weaker than intermolecular forces. London dispersion forces are a weakest intermolecular force which results from the motion of electrons that creates temporary dipoles in molecules.
When the electrons in two adjacent atoms are displaced in a way that atoms get some temporary dipoles, then they attract each other through the London dispersion force. These intermolecular forces occur between non-polar substances and this is the reason that they can condense to liquids and or freeze into solids at low temperature.
These London dispersion forces are often found in the halogens ${F_2}$ or ${I_2}$, the noble gases like Ne and Ar, and in other nonpolar molecules, such as $C{O_2}$ and $C{H_4}$.

B.Dipole-Dipole Forces:
Dipole – dipole interactions are a type of intermolecular attraction that happens between two molecules. Dipole - dipole interactions are electrostatic interactions between the permanent dipoles of different molecules. These interactions align the molecules to increase the attraction.
An example of a dipole – dipole interaction can be seen in HCl (hydrogen chloride) where the relatively positive end of a polar molecule attracts the relatively negative end of another HCl molecule.

C.Dipole – induced Dipole Forces:
A dipole-induced dipole attraction is a weak attraction that results when a polar molecule will induce a dipole in an atom or in a nonpolar molecule by distorting the arrangement of electron clouds of the non-polar species.

Note: When a polar molecule is present, near a nonpolar molecule, the partial charges on the polar molecule causes a distortion of the electron cloud of the other molecule and as a result of this distortion of its electron cloud, the second molecule acquires regions of partial positive and partial negative charges, causing it to become polar. The partial charges that are formed behave just like those of a permanently polar molecule and interact well with their equivalents in the polar molecule that originally induced them. Hence, the two molecules bind together. This interaction also adds to the intermolecular forces in the molecule and affects its reactions/properties.