2. Learning Objectives
• 1. use the molecular structure of water to explain its properties,
• 2. explain the properties of water with its intermolecular forces;
and,
• 3. recognize the important application of the properties of water.
3. • The liquid state of matter is an intermediate phase
between solid and gas.
• Like the particles of a solid, particles in a liquid are
subject to intermolecular attraction; however, liquid
particles have more space between them, so they
are not fixed in position.
• The attraction between the particles in a liquid
keeps the volume of the liquid constant.
4. • The movement of the particles causes the liquid to
be variable in shape. Liquids will flow and fill the
lowest portion of a container, taking on the shape of
the container but not changing in volume.
• The limited amount of space between particles
means that liquids have only very limited
compressibility.
5. Review:
• The three major types of intermolecular
interactions are
dipole–dipole interactions,
London dispersion forces (these two are often
referred to collectively as van der Waals
forces), and
hydrogen bonds. Dipole–dipole interactions
arise from the electrostatic interactions of the
positive and negative ends of molecules with
permanent dipole moments; their strength is
6. Review:
• Dipole–dipole interactions arise from the
electrostatic interactions of the positive and
negative ends of molecules with permanent dipole
moments; their strength is proportional to the
magnitude of the dipole moment and to 1/r3,
where r is the distance between dipoles.
7. Review:
• London dispersion forces are due to the formation
of instantaneous dipole moments in polar or
nonpolar molecules as a result of short-lived
fluctuations of electron charge distribution, which
in turn cause the temporary formation of an
induced dipole in adjacent molecules. their energy
falls off as 1/r6.
8. Review:
• In addition larger atoms tend to be more
polarizable than smaller ones because their outer
electrons are less tightly bound and are therefore
more easily perturbed.
• Hydrogen bonds are especially strong dipole–
dipole interactions between molecules that have
hydrogen bonded to a highly electronegative atom,
such as O, N, or F.
9. Review:
• The resulting partially positively charged H atom
on one molecule (the hydrogen bond donor) can
interact strongly with a lone pair of electrons of a
partially negatively charged O, N, or F atom on
adjacent molecules (the hydrogen bond acceptor).
• Because of strong O⋅⋅⋅H hydrogen bonding
between water molecules, water has an unusually
high boiling point, and ice has an open, cagelike
structure that is less dense than liquid water.
10. What is the strongest intermolecular force present for each of the following
molecules?
1. hydrogen (H2)______________________
2. carbon monoxide (CO) _____________
3. silicon tetrafluoride (SiF4)______________
4. nitrogen tribromide (NBr3) ______________
5. water (H2O)__________________
6. acetone (CH2O) ______________
7. methane (CH4) _______________
8. benzene (C6H6)_______________
9. ammonia (NH3) ________________
10.methanol (CH3OH) ________________
Exercises #1:
London dispersion forces
London dispersion forces
London dispersion forces
Dipole-dipole forces
Hydrogen bonding
Hydrogen bonding
Hydrogen bonding
Dipole-dipole forces
London dispersion forces
London dispersion forces
11. Effects of Intermolecular Forces
• Intermolecular forces control how well
molecules stick together.
• This affects many of the measurable
physical properties of substances
12. Melting and Boiling Points
• If molecules stick together more, they'll be tougher to
break apart.
• The stronger intermolecular forces → higher melting
and boiling points.
• The more electrons a molecule has, the greater the
intermolecular attractions.
• Also, a larger size increases the London dispersion forces.
The increased attraction of the molecules to each other
means that more energy is needed to separate them
from each other. Hence, the boiling point increases.
13. Melting and Boiling Points
• Boiling point is the temperature at which a material
changes from a liquid to a gas (boils) while the melting
point is the temperature at which a material changes
from a solid to a liquid (melts). Keep in mind that a
material's melting point is the same as its freezing point.
14. Viscosity
• Viscosity is a measure of how well substances flow.
• The Stronger intermolecular forces → higher viscosity.
• The viscosity of a liquid is its resistance to flow.
• Liquids that have strong intermolecular forces tend to
have high viscosities.
• Viscosity is another type of bulk property defined as a
liquid’s resistance to flow. When the intermolecular
forces of attraction are strong within a liquid, there is a
larger viscosity.
• https://www.youtube.com/watch?v=9NYs3Y-IjGw
15. Surface Tension
• Surface tension is a measure of the toughness of the surface
of a liquid.
• The stronger intermolecular forces → higher surface
tension or the stronger the intermolecular interactions,
the greater the surface tension.
• Surface tension is the energy required to increase the
surface area of a liquid by a given amount.
• Surface tension is the energy, or work, required to increase
the surface area of a liquid due to intermolecular forces.
• https://www.youtube.com/watch?v=zMzqiAuOSz0
16. Vapor Pressure
• This is a small amount of gas that is found above all
liquids.
• The stronger intermolecular forces → Lower vapour
pressure or the substances with strong intermolecular
forces will have lower vapor pressure, because fewer
molecules will have enough kinetic energy to escape at
a given temperature.
• Substances with high vapor pressures are said to be
volatile - that is, they easily evaporate.
• https://www.youtube.com/watch?v=ffBusZO-TO0
17. Molar Heat of Vaporization
• The heat of fusion (heat required to melt a solid) and
heat of vaporization (heat required to vaporize a liquid)
are determined by the strength of the Intermolecular
Forces.
• Substances with high IMF will have higher melting and
boiling points.
• The molar heat of vaporization is an important part of
energy calculations since it tells you how much energy is
needed to boil each mole of substance on hand.
• https://www.youtube.com/watch?v=ljdv-am0Sis
18. What happened if intermolecular attraction
increases?
• The vapor pressure (the pressure of the vapor that is in
equilibrium with its liquid) decreases.
• The boiling point (the temperature at which the vapor
pressure becomes equal to the pressure exerted on the
surface of the liquid) increases.
• Surface tension (the resistance of a liquid to spread out
and increase its surface area) increases.
• Viscosity (the resistance of a liquid to flow) increases.
19. Write the word TRUE for all numbers that describes correct ideas about buffer
solutions.
1. Melting and boiling points molecules stick together more, they'll be
tougher to break apart because the stronger intermolecular forces →
higher melting and boiling points.
2. The more electrons a molecule has, the greater the intermolecular
attractions. Also, a larger size increases the Dipole–dipole interactions.
3. Viscosity is a measure of how well substances flow.
4. The weaker intermolecular forces → higher viscosity.
5. Liquids that have strong intermolecular forces tend to have high viscosities.
Exercises #2:
20. 6. Surface tension is a measure of the toughness of the surface of a liquid.
7. The stronger intermolecular forces → higher surface tension or the stronger.
8. Vapour pressure this is a small amount of gas that is found above all liquids.
9. The stronger intermolecular forces → Lower vapour pressure or the
substances with strong intermolecular forces will have lower vapor
pressure, because fewer molecules will have enough kinetic energy to
escape at a given temperature.
10. Heat of vaporization or heat required to vaporize a liquid are determined by
the strength of the Intermolecular Forces.
Exercises #2:
22. •THE PROPERTIES OF WATER
•Water is an inorganic compound that is
colorless, odorless, tasteless, but it is
considered as the most important
compound in the body. In fact, 50% of
water or more is in the normal adult`s
body.
•The capability of dissolving more
substances than any other liquid made
water as “universal solvent”.
23. •THE MAIN PROPERTIES OF WATER
•Polarity
•Cohesion
•Adhesion
•surface tension
•high specific heat
24. •THE PROPERTIES OF WATER
•A water molecule is made
up of two hydrogen atoms
bonded to an oxygen atom.
Each end of a water
molecule has a slight
electric charge.
•A molecule that has
electrically charged areas is
called a polar molecule.
25. • This uneven distribution of charges
across a molecule making one end
positive (H) and the other negative (O)
is called polarity.
• The positive hydrogen ends of one
water molecule attract thenegative
oxygen ends of nearby water
molecules causing them to stick
together like weak magnets.
• This attraction causes water molecules
to form temporary bonds that break
easily. They are called hydrogen bonds.
