Inter molecular forces

1. Types of
Intermolecular
Forces- London
Dispersion, Dipole–
Dipole, Hydrogen
Bonding

2. The properties of
liquids are
intermediate between
those of gases and
solids, but are more
similar to solids.

3. Intermolecular forces determine bulk properties,
such as the melting points of solids and the boiling
points of liquids. Liquids boil when the molecules
have enough thermal energy to overcome the
intermolecular attractive forces that hold them
together, thereby forming bubbles of vapor within
the liquid. Similarly, solids melt when the molecules
acquire enough thermal energy to overcome the
intermolecular forces that lock them into place in
the solid.

4. Intermolecular forces are electrostatic in nature;
that is, they arise from the interaction between
positively and negatively charged species. Like
covalent and ionic bonds, intermolecular
interactions are the sum of both attractive and
repulsive components. Because electrostatic
interactions fall off rapidly with increasing
distance between molecules, intermolecular
interactions are most important for solids and
liquids, where the molecules are close together.
These interactions become important for gases
only at very high pressures, where they are

5. 1. Dipole-Dipole Interaction
Dipole-dipole interaction exists between the
differently charged particles of a molecule. In other
words, the interconnection that lies within a part of a
molecule that is partially negatively charged and
another part of a molecule that is partially positively
charged is called a dipole-dipole interaction. The only
requirement of such interaction force to exist is that
the elements must be charged with different polarity
charges. These are the strongest intermolecular
forces of attraction existing in nature. For example, a
dipole-dipole force of attraction helps to bind a
hydrogen atom with a chlorine atom to form a

7. 2. Hydrogen Bonding
Hydrogen bonding is a special case of dipole-dipole
interaction. It specifically occurs when a hydrogen
atom is bonded to a nitrogen, oxygen, or fluorine
atom. Hydrogen consists of a partially positive charge,
whereas oxygen, fluorine, or nitrogen are partially
negatively charged. This difference in the polarity of
charges on the atoms establishes a force of attraction,
which is responsible for a hydrogen bond to exist
between them. It is highly difficult to break hydrogen
bonds and therefore requires a lot of energy. Some
examples of a hydrogen bond are water (H2​O) and
hydrogen fluoride (HF). This is the reason why the

9. 3. London Dispersion Forces
London dispersion forces occur between
temporary or induced dipoles. It is a temporary
force of attraction that exists between the
electrons of two adjacent atoms. These are the
weakest of all the intermolecular forces.
London dispersion force is proportional to the
number of electrons contained by a molecule.
They are a part of van der Waals forces. The
more be the London dispersion force, the more
will be the boiling point of the compound.
These forces do not require a huge amount of

11. VAN DER WAALS
FORCES:
Van der waals forces are the weak forces
that contribute to the intermolecular
bonding between molecules.
Molecules inherently possess energy and
their electrons are always in motion, so
transient concentration of electrons in
one region
Of a molecule to be attracted to the
electrons of another molecule. Similarly,
negatively charged regions of another

12. KEY TAKE AWAYS: VAN DER WAALS FORCES
• Van der Waals forces are distance-
dependent forces between atoms and
molecules not associated with covalent
or ionic chemical bonds
• Sometimes the term is used to
encompass all intermolecular forces,
although some scientists only include
among them the London dispersion
force.
• Van der Waals forces are the weakest of

13. PROPERTIES OF VAN DER WAALS FORCES
• They are additive
• They are weaker than either ionic or
covalent chemical bonds.
• They are not directional
• They act only over a short range. The
interaction is greater when molecules
draw closer.
• They are independent of
temperature, with the exception of
dipole-dipole interactions.

14. 4 MAJOR CONTRIBUTIONS OF VAN DER WAALS FORCE
1.A negative component prevents molecules
from collapsing. This is due to Pauli exclusion
principle
2.Either an attractive or a repulsive electrostatic
interaction occurs between permanent charges.
3.Induction or polarization occurs. This is the
attractive forces between permanent polarity
on one molecule and an induced polarity on
another.
4.London dispersion forcer is the attraction
between any pair of molecules due to
instantaneous polarization.

15. Examples:
1. DNA
Deoxyribonucleic Acid or
DNA is a chemical
compound that stores all the
genetic information of a
living being. Hydrogen
bonding is responsible for
the existence of a DNA
molecule. A strong force of
interaction existing between
the four parts, namely

16. 2. Proteins
Proteins are long chain polymers
made up of amino acids. These long
chains are known as polypeptides.
They play a key role in the life of all
living beings. The primary structure of
proteins is formed by the covalent
bond existing between the amino acid
molecules. The secondary structure is
made up of the hydrogen bonding
present between the different
sections of the protein chain. The
process with which a protein
compound folds and forms its tertiary

17. 3. Plants
The movement of water through the
xylem and other parts of a plant
makes use of hydrogen bonding.
Plants containing tiny and rigid tubes
that are made up of cellulose. A
strong adhesive force exists between
water and the cellulose walls. This
force supports the capillary action
that is used to supply nutrients and
fluids to the stem, trunk, and other
parts of a plant. Hydrogen bonding is
responsible for the upward

18. 4. Soap and Detergents
The soap bubbles are made up
of soap molecules and water
molecules. Water is a polar
molecule, whereas a soap
bubble has a polar and non-
polar end. The polar ends of
both the molecules get
attracted to each other, which
helps in the establishment of
an intermolecular force. This
intermolecular interaction is

19. 5. Water
Water is composed of hydrogen and
oxygen atoms. The atoms are bonded
to each other using the hydrogen
bond. A hydrogen bond is a special
form of the dipole-dipole bond that
exists between partially positive
hydrogen and partially negative oxygen
of another molecule. The
intermolecular force existing within the
compounds helps the water molecules
to stick to each other. The hydrogen
bond is the strongest intermolecular
bond, which is why it is difficult to