The document discusses the three main types of intermolecular forces: dipole-dipole forces, London dispersion forces, and hydrogen bonding. It describes each type of force, including that dipole-dipole forces exist between polar molecules, London dispersion forces exist between all molecules, and hydrogen bonding specifically refers to the attraction between hydrogen atoms bonded to electronegative atoms like N, O, or F. The document also discusses how these intermolecular forces can explain the physical properties of liquids and some solids.

1. Many of the physical properties of liquids (and
certain solids) can be explained in terms of
intermolecular forces, the forces of attraction
between molecules.
Intermolecular forces
– Three types of forces are known to exist between
neutral molecules.
1. Dipole-dipole forces
2. London (or dispersion) forces
3. Hydrogen bonding

2. 2
Dipole-Dipole Forces
Orientation of Polar Molecules in a Solid
So higher dipole, larger attractive force.
Dipole-dipole forces are attractive forces between the positive
end of one polar molecule and the negative end of another
polar molecule. Dipole-dipole forces have strengths that range
from 5 kJ to 20 kJ per mole. They are much weaker than ionic
or covalent bonds and have a significant effect only when the
molecules involved are close together

3. •Polar molecules have a partial negative end and a partial
positive end.
•The partially positive end of a polar molecule is attracted to
the partially negative end of another .

4. 4
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
Ion-Dipole Interaction
Small r, larger F

5. •An ion-dipole force is an attractive force that results
from the electrostatic attraction between an ion and
a neutral molecule that has a dipole.
•Most commonly found in solutions. Especially
important for solutions of ionic compounds in polar
liquids.
•A positive ion (cation) attracts the partially negative
end of a neutral polar molecule.
•A negative ion (anion) attracts the partially positive
end of a neutral polar molecule.
•Ion-dipole attractions become stronger as either the
charge on the ion increases, or as the magnitude of
the dipole of the polar molecule increases.

6. 6
Dispersion Forces
ion-induced dipole interaction
dipole-induced dipole interaction
(also be called as London Force)
(induced-induced dipoles interaction)

7. 7
Hydrogen Bond
A hydrogen bond is the attraction between the lone pair of an
electronegative atom and a hydrogen atom that is bonded to either
nitrogen, oxygen, or fluorine.[3] The hydrogen bond is often described
as a strong electrostatic dipole-dipole interaction. However, it also has
some features of covalent bonding: it is directional, stronger than a
van der Waals interaction, produces interatomic distances shorter
than the sum of van der Waals radius, and usually involves a limited
number of interaction partners, which can be interpreted as a kind of
valence.

8. It arising from interactions between rotating permanent
dipoles and from the polarizability of atoms and molecules
(induced dipoles). These induced dipoles occur when one
molecule with a permanent dipole repels another
molecule’s electrons. A molecule with permanent dipole
can induce a dipole in a similar neighboring molecule and
cause mutual attraction.
What is induced dipole ?

10. 10
S
What type(s) of intermolecular forces exist
between each of the following molecules?
HBr
HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces
between HBr molecules.
CH4
CH4 is nonpolar: dispersion forces.
SO2
SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between
SO2 molecules.

11. Theory of liquids
• Bernal and scott theory
 This theory tells about the random packing of
the liquid molecules.