Chapter 11
Intermolecular Forces, Liquids, and
Solids
Warm Up
C
A
B
Which has highest KE?
How does attraction between atoms change with KE?
Agenda
• What are the types of intermolecular forces?
How do they influence physical properties?
• IMF’s
• Physical properties influenced by IMF’s
• Phase changes
HW Ch 11: 2, 7, 9, 11, 12, 15-47 odds
Intermolecular Forces
• Although weak; strong enough to control
physical properties such as boiling and melting
points, vapor pressures, and viscosities.
Ion-dipole Forces
• Ion and polar molecule.
• Sodium chloride dissolves
in water.
O of water
Na attracted to ____
H of water.
Cl attracted to _____
Dipole – Dipole Forces
• Neural polar molecules and liquid or solid
state.
• Water (H2O) and
Methanol (CH3OH)
London Dispersion Forces
• Attractions between induced dipoles.
• Nonpolar covalent molecules and atoms have
attractive forces due to an induced dipole.
The positive nucleus of one atom attracts the
electrons of another.
• Weakest of intermolecular forces!
Factors Affecting London Forces
• The strength of dispersion forces tends to
increase with increased molecular weight.
• Larger atoms have larger electron clouds, which
are easier to polarize.
Hydrogen Bonding
• Especially strong dipole-dipole.
Exists between hydrogen atoms bonded to O, F,
or N of one molecule, with an O, F, or N of
another molecule.
H is small and can get very close to the lone
pairs of these electronegative atoms.
Question
• In which of these substances is H bonding
likely to play an important role in determining
physical properties?
CH4
H2NNH2
CH3F
CH3COCH3
H2O
Summarizing Intermolecular Forces
IMF’s affect physical properties
• Viscosity – the resistance of a liquid to flow.
For related compounds, viscosity increases
with molar mass.
• It is related to the ease with which molecules
can move past each other.
• Viscosity increases with stronger
intermolecular forces and decreases with
higher temperature… (WHY??)
IMF’s affect physical properties
• Surface tension – energy required
to increase the surface area of a liquid
by a unit amount.
• Imbalance of intermolecular forces at surface
of the liquid
IMF’s affect physical properties
• Cohesive Forces – IMF’s that bind similar
molecules to one another (H bonding in
water)
• Adhesive forces – binds a substance to a
surface. Why a meniscus occurs!
Warm – Up!
• Name the all the IMF’s involved in each of the
following molecules
• Aqueous NaCl
• FeBr3
• HF
• Aquesous solution of CH3OH
Agenda
• Questions for today:
• What is vapor pressure and how do
intermolecular forces impact vp?
• How do you read phase diagrams?
• How do molecules organize themselves in
solids?
• Ch 11: 49, 51, 55, 57, 69-75 odds
Phase Changes
Which are endothermic and which are exothermic?
Heating Curve
Hvap
Hfus
Temp does not change during melting of vaporization.
Vapor Pressure
• Liquids of low molar mass and weak IMF’s tend to
have high vapor pressures.
• As temp increases KE increases and VP increases.
Vapor Pressure
Substances with high vapor pressure are “volatile”
They evaporate quickly!
Question
Which liquid is more volatile?
CCl4 or CBr4
And why??
Phase Changes
• Critical temperature – highest temperature at
which a liquid can exist. Higher than critical
temperature, substances are in the gas state.
• Critical pressure – pressure required to bring
about liquefaction at the Tc.
• Nonpolar and low MW have low Tc and Pc.
• Polar and high MW have higher Tc and Pc.
Phase Diagrams
• (a) What does point V represent? What characteristics
are specific to the system only at point V?.
• (b) What does each point on the curve between V and W
represent?
• (c) Describe the changes that the system undergoes as
the temperature slowly increases from X to Y to Z at 1.0
atmosphere.
• (d) In a solid-liquid mixture of this substance, will the
solid float or sink? Explain.
Bonding in Solids
• Molecular solids – held together by weak IMFs;
soft and low melting
Phosphorous changes form with heat and pressure!
Bonding in Solids
• Covalent-network solids – held together by large
networks or chains of covalent bonds. Hard high
melting (examples: diamond and graphite for C,
and quartz for SiO2)
Bonding in Solids
• Ionic solids - held together by strong ionic
bonds, brittle and high melting.
NaCl
Bonding in Solids
• Metallic solids – only metal atoms held
together by attraction of metal nuclei to
delocalized electrons throughout the solid.
Metals don’t have enough
electrons for everyone to have
their own, so the electrons are
delocalized throughout all the
metal atoms which makes
metallic solids great conductors.
Steel
Conduction in Metal Solids
Warm Up
For the ClF3 molecule:
1. Draw the Lewis structure and make a rough 3-D
sketch.
2. Identify the orbital hybridization, the electrondomain geometry and the molecular geometry.
3. Identify the approximate bond angles.
4. Predict if it is a polar species. Justify your answer.
5. Predict the most probable oxidation number of
the chlorine atom
Agenda
•
•
•
•
Ch 11 Practice and review
Go over free response on Ch 8-9 quiz
Quiz corrections due 11/30
Lab Due Tuesday 11/22
2001 D Required
• Answer the questions below that relate to the five aqueous
solutions at 25 C shown above.
• (a) Which solution has the highest boiling point? Explain.
• (b) Which solution has the highest pH? Explain.
• (c) Identify a pair of the solutions that would produce a
precipitate when mixed together. Write the formula of the
precipitate.
• (d) Which solution could be used to oxidize the Cl–(aq) ion?
Identify the product of the oxidation.
• (e) Which solution would be the least effective conductor of
electricity? Explain.
2001 Answers
• (a) solution 1, Pb(NO3)2. This compound will dissociate into
three ions with the highest total particle molality. The greater
the molality, the higher the boiling point. Solutions 2, 3, and 5
will produce two ions while solution 4 is molecular.
• (b) solution 5, KC2H3O2. The salt of a weak acid (in this case,
acetic acid) produces a basic solution, and, a higher pH.
• (c) solution 1, Pb(NO3)2, and solution 2, NaCl. PbCl2
• (d) solution 3, KMnO4 , ClO3–
• (e) solution 4, C2H5OH. Ethyl alcohol is covalently bonded and
does not form ions in water. Therefore, the solution is not a
better conductor of electricity than water, which is also
covalently bonded.
Acetone  CH3COCH3
1. Draw the Lewis structure for acetone and
predict the geometry around each C atom.
2. Is acetone polar or nonpolar? Why?
3. What types of IMF’s exist for acetone?
4. 1-propanol CH3CH2CH2OH boils at 97.2 °C
and acetone boils at 56.5 °C. Explain this
difference.
Think about…
• How does sweating cool you off?
• A flask of water is connected to a vacuum
pump. A few moments after the pump is on,
the water begins to boil. After a few minutes,
the water then freezes. Explain.
• For each of the following, use appropriate chemical
principles to explain the observations. Include chemical
equations as appropriate.
• (a) In areas affected by acid rain, statues and structures
made of limestone (calcium carbonate) often show signs of
considerable deterioration.
• (b) When table salt (NaCl) and sugar (C12H22O11) are
dissolved in water, it is observed that
(i)
both solution have higher boiling points than
pure water, and
(ii)
the boiling point of 0.10 M NaCl(aq) is higher
than that of 0.10 M C12H22O11(aq).
• (c) Methane gas does not behave as an ideal gas at low
temperatures and high pressures.
• (a) limestone reacts with acid to produce a soluble substance, a
gas, and water which wash away
•
CaCO3(s) + H+(aq) ® Ca2+(aq) + CO2(g) + H2O(l)
• (b) (i) a solution made from a non-volatile solute has a higher
boiling point than the pure solvent because the solution has a lower
vapor pressure than the water (Raoult’s Law) . the temperature of
the solution has be higher to produce enough vapor pressure to
equal the atmospheric pressure (i.e., boiling)
•
(ii) the amount of boiling point elevation depends on the
number of non-volatile particles in solution. since the salt
dissociates into 2 particles for every NaCl that dissolves, it will
increase the boiling point more that an equal concentration of
sugar (a molecular cpd) that does not dissociate or ionize.
• (c) at low temperatures and high pressures, the methane
molecules are slow and closer together. under these conditions, van
der Waal forces become measurable and significant and creates a
deviation from ideal behavior. at high pressure the volume of a real
molecule is also significant.
• (d) a water vapor molecules collide with the cool beaker, the
molecules lose kinetic energy, slow down, attract others, and
condense into a liquid