Physical states of matter

1. PHYSICAL STATES OF MATTER
LIQUIDS

2. Physical properties of liquids:
 Liquid state may be regarded as intermediate between gaseous
and solid state of matter
 No definite shape
 Definite volume
 Density much greater than gases
 Molecules in liquid are in constant state of motion but they are in
contact with each other. The forces of attraction between
molecules are strong enough to hold them together and the
molecules are able to move past one another through available
intermolecular spaces. Molecules in liquid move in random
fashion,at any instant molecules may form clusters leaving vacant
space/hole here and there.
 Most of the physical properties of liquids are governed by the
strength of intermolecular forces of attraction.
What are liquids?
A liquid may be defined as the collection of molecules held
close to each other and executing random motion through
intervening spaces.

3. INTERMOLECULAR FORCES IN
LIQUIDS:
Vander Waals forces
Dipole-dipole attractions
London forces
Hydrogen bonding
INTERACTIONS AMONG THE
MOLECULES IN LIQUIDS

4. Exist between polar molecules
Presence of polar bonds
Unsymmetrical molecule
One of the stronger intermolecular
attractions
DIPOLE-DIPOLE ATTRACTIONS

5.  Exist in non-polar molecules, result from
temporary charge imbalances
 The temporary charge exist because the
electrons in a molecule or ion move randomly
in the structure.
 The nucleus of one atom attracts electrons
from the neighboring atom. At the same time
the electrons in one particle repel the
electrons in the neighbor and create a short
range charge imbalance, also called short
range forces.
LONDON DISPERSION FORCES

6.  These temporary charges in one
molecule/atom attracts opposite
charges in nearby molecules/atoms. A
local slight positive charge in one
molecule will be attracted to a
temporary slight negative charge in
neighboring molecule.
 Also called instantaneous dipole induced
dipole forces.

7.  Unique type of intermolecular attraction
defined as “the electrostatic force of
attraction between an electronegative
atom and partial positively charged
hydrogen atom”.
 Covalent bond between hydrogen atom &
either F,O,N(the most electronegative
atoms)
 Interaction of the H-atom in this kind of
polar bond with a lone pair of electrons on
a nearby atom like F,O,N
HYDROGEN BONDING

8.  Cleansing action of soaps and detergents is
due to the polar part of their molecules are
water soluble due to hydrogen bonding
 Hydrogen bonding is present in the molecules
of living systems such as proteins and DNA.
 Hydrogen bonding is also present in food
materials like carbohydrates such as glucose
as they all have OH groups in them which are
responsible for hydrogen bonding
 It is also present in cotton, silk, fiber and
thread making materials.
Hydrogen bonding is responsible of the
expansion of water when it freezes.

9. The process by which molecules of a liquid go into the
gaseous state(vapors) is called vaporization/evaporation
& the reverse process is called condensation.
How evaporation causes cooling?
Molecules in a liquid move with different K.E.
The molecules which have low K.E. move slowly while
others with high K.E. overcome the intermolecular
forces of attractions & leave the bulk of liquid as it
reaches the surface and escape leaving behind low
energy molecules, the temperature of liquid falls and
heat moves from the surrounding to the liquid and then
the temperature of surrounding also falls.
EVAPORATION/VAPOURISATION

10. Surface area
Temperature
Intermolecular forces
Factors affecting rate of evaporation

11. The vapour pressure of a liquid is
defined as the pressure exerted by
the vapour in equilibrium with the
liquid at a given temperature.
Liquid Vapor
Vapour pressure

12. The vapor pressure of any substance increases
as its temperature increases because at
elevated temperature the K.E. of molecules is
enhanced which overcomes the intermolecular
forces of attractions and hence the capability to
leave surface increases.
Attractive forces are stronger in polar
molecules such as water and have relatively low
vapor pressure where as non-polar molecules
such as ethanol & ether have weak
intermolecular forces & high vapor pressure.
Effect of temperature on vapor
pressure

13.  STATIC METHOD
Barometric method
Manometric method
 DYNAMIC METHOD
Ramsay & young’s method
Determination of vapor pressure

14. When a liquid is heated, tiny bubbles are formed
in it due to increase in vapor pressure. A stage
reaches when vapor pressure of liquid becomes
equal to the external atmospheric pressure. This
temperature is called boiling point of that liquid.
The reason for this is the bubbles of vapors
which are formed in the interior of liquid have
greater internal pressure than atmospheric
pressure on the surface of liquid due to which
bubble comes out of the liquid & burst upon the
surface.
Effect of vapor pressure on boiling
points

15. Molecules in interior of a liq. are attracted
equally in all directions by molecules around it,&
are subjected to balanced set of forces,
whereas molecules at the surface are attracted
only towards the interior. These attractions pull
the surface layer towards the center because of
the difference in the strength of interactions of
the surface molecules with the molecule in
vapor phase & the one that is below in the bulk.
SURFACE TENSION

16.  A droplet assumes a spherical shape because
a sphere has the minimum surface area for a
given volume.
 Surface tension is defined as the force in
dynes acting along the surface of a liquid at
right angle to a unit length(1cm).
 Units: SI system; N/m
 CGS system; dynes/cm
As a result of inward attraction the surface of liquid
experience an attractive force known as Surface
Tension, ɣ

17.  Surface tension decrease with increase in
temp due to decrease in intermolecular
forces.
 Capillary action of liquids
Cohesive forces
Adhesive forces
Contact angle,θ
Effect of temperature on surface
tension

18.  Capillary rise method
 Drop formation method(stalagmometer)
 Du Noye torsion/tensitometer/ring
detachment method
Applications:
Soaps & detergents
Methods for the determination of
surface tension

19. The internal resistance to flow of a liquid is
called viscosity(Ƞ).
It may be defined as,
The force of resistance per unit area which will
maintain unit velocity difference between two
layers of a liquid at a unit distance from each
other.
Reciprocal of viscosity is called fluidity.
VISCOSITY

20. Method for determination of viscosity-The Ostwald’s
Viscometer.
Effect of temp. on viscosity:
Viscosity decrease with increase in temperature
Applications:
Manufacture of,
 Syrups, suspensions
 Paints
 Polymers
 Glue
Units: Poise(P) & Centipoise (CP)

21. It is defined as “the ratio of velocity of light in
vacuum or air to that in the substance.”
When ray of light passes from air to liquid its
direction is changed n this change of direction is
called refraction. The refractive index given by
Snelle’s law,
n=Sin i/Sin r
REFRACTIVE INDEX(n)

22.  Abbe refractometer
Applications: LCD, optical fibers & polymers used in
optical lenses
Optical activity
A beam of ordinary light consist of electromagnetic
waves oscillating in many planes, when this light passed
through a polarizer, only waves oscillating in single
plane pass through, called plane polarized light.
 Optically active compounds
 Levo & Dextrorotatory compounds
 Specific rotation/angle of rotation
Determination of refractive index