kinetic molecular theory

1. • As identified in General Chemistry 1, matter
exists in three different phases solid, liquid and
gas. Some matter can also exist in all three states.
One example is water. At room temperature,
water is a liquid, and the molecules in it move
slowly. When water is heated, its liquid state will
change to gas; the molecules will be moving very
fast and taking up space everywhere. When heat
is reduced, the vapor molecules slow down and
gradually turn back into liquid. When frozen, the
molecules will be extremely slow and move very
little. They will hold on to each other turning the
water into a solid. Lastly, placing the ice at room
temperature will make the ice a liquid.

2. • You have previously learned that matter has
different characteristics. Ice melts easier than
salt; ethanol evaporates faster than water;
hexane has a higher boiling point than
methane; and salt is soluble in water but not
in nonpolar liquids.
• In Chemistry 2, you will go beyond these and
discuss the various intermolecular forces of
attraction in association to these properties of
liquids and solids.

4. SOLID
1. Closely packed and orderly arranged.
2. Particles vibrate and rotate about a fixed
position.
3. Moves very slow.
4. Attractive force between particles are very
strong.

5. LIQUID
1. Less closely packed than in a solid and
disorderly arranged.
2. Particles slide over each other.
3. Motion of particle is low.
4. Has a strong attractive forces between
particles.

6. GAS
1. Particles are very far apart and disorderly
arranged.
2. Particles move about at great speed.
3. Motion of particle is high.
4. Has a very weak attractive forces.

7. INTRAMOLECULAR FORCES
• Exists inside the molecule.
• Maybe ionic ( attraction between cations and
anions), covalent ( sharing of electrons), and
metallic ( attraction between metal cations
and delocalized valence electrons).

8. INTERMOLECULAR FORCES
• Occur between neighboring molecules as a
result of partial charges or between ions and
molecules.
• Usually called Van der Waals forces
• The types are ion-dipole, Dipole-dipole,
London dispersion, H- bond.

9. ION – DIPOLE FORCES
• Results when an ion and the partial charge
found at the end of a polar molecule attract
each other.
• Important in solutions of ionic substances.
• Example: Calcium chloride, Sodium oxide,
Aluminum bromide.

11. DIPOLE – DIPOLE FORCES
• Weaker than an ion-dipole.
• Polar molecules attract each other when unlike
charges are close together and repel each other
when like charges are close together. Example are
HCl, PCl3, H2Se.
• Between two polar molecules
• The more polar the substance, the stronger its
dipole-dipole interaction.
• The higher the dipole moment, the higher the
boiling point.

13. LONDON DISPERSION FORCES
• More common in nonpolar molecules like Cl2,
He, CH4, and CO2.
• As London dispersion forces increase, the
boiling and melting points of covalent
substances increase with increasing molecular
mass.
• The longer the chain, the higher the boiling
point like in C2H6 and C5H12

15. H - BONDS
• Interaction between a hydrogen atom bonded
to an electronegative F, O, or N atom.
• Stronger than dipole-dipole forces and
dispersion forces.
• H – bond in hydrogen compounds has an
increase boiling point due to increased
dispersion forces.

17. Dipole – Induced Dipole
• For polar and nonpolar molecules
• In the presence of a polar molecule, a
nonpolar molecule is forced to become a
dipole.
• The attractive force that predominates
between an ion and a nonpolar molecule.
• Example is between HCl and O2 molecule

19. PROPERTIES OF LIQUIDS
Due to intermolecular forces liquids exhibit the
following properties:
1. Viscosity
2. Surface Tension
3. Capillarity
4. Evaporation
5. Vapor pressure
6. Boiling point

20. VISCOSITY
• The ability of a fluid to resist flowing.
• Nonpolar molecules like benzene (C6H6),
pentane (C5H12) and carbon tetrachloride
(CCl4)have low viscosities due to weak
intermolecular forces (London dispersion).
• Polar molecules like glycerol (C3H5(OH)3) and
syrup have high viscosities because of H-
bonding among their –OH groups.

21. • The viscosity of a liquid decreases with
increasing temperature because the average
kinetic energy of molecules is greater.
• Viscosity can be measured using a viscometer.

23. SURFACE TENSION
• The energy required to increase the surface area
of a liquid.
• An example are small insects walk on bodies of
water, needles float on water and water beaded
up on a newly waxed car.
• These happen due to unequal intermolecular
forces at the surface of the liquid. To increase the
surface area of a liquid, molecules move to the
surface by breaking some attractions in the
interior which requires energy (surface tension).

24. • Surfactants (surface-active ingredients) such
as detergents, soaps and biological fat
emulsifiers decrease the surface tension of
water and destroy H-bonds.

27. CAPILLARITY
The rising of the blood or any liquid in a tube is
called capillarity or capillary action.
It is observed when you go for simple blood tests
and in the transport of water from the roots of a
plant.
This results from a competition between the
intermolecular forces within the liquid molecules
(cohesive forces) and those between the liquid
molecules and the walls of the tube (adhesive
forces).

28. COHESIVE force – the attractive force between
molecules of the same substance.
ADHESIVE force – the attractive force between
molecules of different substances.

31. Evaporation, Vapor Pressure and
Boiling Point
• Evaporation is the escape of a liquid particles
into the gaseous or vapor state.
• The escape of a more energetic molecules on
a liquid surface reduces the average kinetic
energy of the remaining molecules, this
causes the cooling effect when perspiration
evaporates from the skin’s surface like in
alcohol or acetone.

32. • When molecules of liquid in a closed
container reach equilibrium with its vapor
after some time, there is no more change in
the liquid level (saturated vapor pressure).
• However, as the vapor particles increase,
some collide with the liquid surface and return
to the liquid state (condensation).

33. • Volatility is the ability of a substance to
vaporize. It is proportional to its vapor
pressure. The higher the vapor pressure, the
more volatile the liquid.
• An increase in temperature decreases the
intermolecular force of attraction in a liquid,
thereby also increasing vapor pressure.

34. Boiling point is the temperature wherein
the saturated vapor pressure is equal to the
external pressure. This property changes as
pressure changes. The effect of high altitudes
and lower boiling point temperature can be
counteracted by using a pressure cooker.

35. Properties of Water
1. Water has high surface tension.
2. Water has high boiling point.
3. The density of solid water or ice is less than the
density of liquid water due to the stronger H-
bond in ice.
4. Water has a high heat of vaporization ( the
amount of heat required to change a given
amount of liquid into gas).
5. Water is a good solvent due to its polar nature.

36. ASYNCHRONOUS ACTIVITY
Answer Activity 1.1 p6
Activity 1.2 p9