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CH 11: INTERMOLECULAR FORCES AND TYPES OF SOLIDS
Brown, LeMay
AP Chemistry
Monta Vista High School
Credits: Adapted from Kotz, Weaver and Trichel’s PPT
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INTER-INTER-MOLECULAMOLECULAR FORCESR FORCES
INTER-INTER-MOLECULAMOLECULAR FORCESR FORCES
Have studied Have studied INTRAINTRAmolecular molecular forces—the forces holding forces—the forces holding atoms together to form atoms together to form molecules.molecules.
Now turn to forces between Now turn to forces between molecules —molecules —
INTERINTERmolecular forces. molecular forces.
Forces between molecules, Forces between molecules, between ions, or between between ions, or between molecules and ions.molecules and ions.
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11.1: INTERMOLECULAR FORCES (IMF)
IMF < intramolecular forces (covalent, metallic, ionic bonds)
IMF strength: solids > liquids > gases Boiling points and melting points are good
indicators of relative IMF strength.
3
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SUMMARY OF INTERMOLECULAR FORCESSUMMARY OF INTERMOLECULAR FORCESSUMMARY OF INTERMOLECULAR FORCESSUMMARY OF INTERMOLECULAR FORCES
Ion-Ion forcesIon-Ion forcesIon-dipole forcesIon-dipole forcesDipole-dipole forcesDipole-dipole forces
Special dipole-dipole force: Special dipole-dipole force: hydrogen bonds (sometimes hydrogen bonds (sometimes treated as a separate IMF)treated as a separate IMF)
Forces involving non polar Forces involving non polar molecules: molecules: induced forces induced forces (LDFs)(LDFs)
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INTERMOLECULAR FORCES SUMMARYINTERMOLECULAR FORCES SUMMARY
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11.2: TYPES OF IMF
1. Electrostatic forces: act over larger distances in accordance with Coulomb’s law
a. Ion-ion forces: strongest; found in ionic crystals (i.e. lattice energy)
6
2d
QQF
http://chemmovies.unl.edu/ChemAnime/IONSIZED/IONSIZED.html Ion size and LE
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b. Ion-dipole: between an ion and a dipole (a neutral, polar molecule/has separated partial charges)
7
Increase with increasing polarity of molecule and increasing ion charge.
2d
QQF
Cl-
S2-<
Ex: Compare IMF in Cl- (aq) and S2- (aq).
http://chemmovies.unl.edu/ChemAnime/NACL1D/NACL1D.htmlNaCl dissolving in Water
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ATTRACTION BETWEEN IONS ATTRACTION BETWEEN IONS AND PERMANENT DIPOLESAND PERMANENT DIPOLESATTRACTION BETWEEN IONS ATTRACTION BETWEEN IONS AND PERMANENT DIPOLESAND PERMANENT DIPOLES
Water is highly polar Water is highly polar and can interact and can interact with positive ions with positive ions to give to give hydratedhydrated ions in water.ions in water.
HH
water dipole
••
••
O-
+
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ATTRACTION BETWEEN IONS ATTRACTION BETWEEN IONS AND PERMANENT DIPOLESAND PERMANENT DIPOLESATTRACTION BETWEEN IONS ATTRACTION BETWEEN IONS AND PERMANENT DIPOLESAND PERMANENT DIPOLES
Attraction between ions and dipole depends Attraction between ions and dipole depends on on ion chargeion charge and and ion-dipole distanceion-dipole distance..
Measured by ∆H for MMeasured by ∆H for Mn+n+ + H + H22O O ff [M(H [M(H22O)O)xx]]n+n+
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c. Dipole-dipole: weakest electrostatic force (Not all IMFs, LDFs weaker than dipole-dipole); exist between neutral polar molecules
10
Increase with increasing polarity (dipole moment) of molecule
Ex: What IMF exist in NaCl (aq)?
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DIPOLE-DIPOLE FORCESDIPOLE-DIPOLE FORCESDIPOLE-DIPOLE FORCESDIPOLE-DIPOLE FORCES
Influence of dipole-dipole forces is seen in Influence of dipole-dipole forces is seen in the boiling points of simple molecules.the boiling points of simple molecules.
CompdCompd Mol. Wt.Mol. Wt. Boil PointBoil Point
NN22 2828 -196 -196 ooCC
COCO 2828 -192 -192 ooCC
BrBr22 160160 59 59 ooCC
IClICl 162162 97 97 ooCC
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PARTNER ACTIVITY
Discuss with your partner the difference between ion-dipole and dipole-dipole interactions, in terms of the following:
- How they are formed- Strength- Examples
12
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d. Hydrogen bonds (or H-bonds): H is unique among the elements because it has a
single e- that is also a valence e-. When this e- is “hogged” by a highly EN atom (a very
polar covalent bond), the H nucleus is partially exposed and becomes attracted to an e--rich atom nearby.
http://www.youtube.com/watch?v=LGwyBeuVjhU
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H-bonds form with H-X•••X', where X and X' have high EN and X' possesses a lone pair of e-
X = F, O, N (since most EN elements) on two molecules:
14
F-H
O-H
N-H
:F
:O
:N
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HYDROGEN BONDINGHYDROGEN BONDINGHYDROGEN BONDINGHYDROGEN BONDING
A special form of dipole-dipole attraction, A special form of dipole-dipole attraction, which enhances dipole-dipole attractions.which enhances dipole-dipole attractions.
H-bonding is strongest when X and Y are N, O, or FH-bonding is strongest when X and Y are N, O, or F
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H-bonds explain why ice is less dense than water.
16http://en.wikipedia.org/wiki/Water_%28molecule%29#Density_of_water_and_ice
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EX: BOILING POINTS OF NONMETAL HYDRIDES
17
Boili
ng P
oin
ts (
ºC)
Conclusions:
Polar molecules have higher BP than nonpolar molecules
∴ Polar molecules have stronger IMF
BP increases with increasing MW
∴ Heavier molecules have stronger IMF
NH3, H2O, and HF have unusually high BP.
∴ H-bonds are stronger than dipole-dipole IMF
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H-BONDING BETWEEN METHANOL AND H-BONDING BETWEEN METHANOL AND WATERWATERH-BONDING BETWEEN METHANOL AND H-BONDING BETWEEN METHANOL AND WATERWATER
H-bondH-bondH-bondH-bond--
++
--
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H-BONDING BETWEEN TWO METHANOL H-BONDING BETWEEN TWO METHANOL MOLECULESMOLECULESH-BONDING BETWEEN TWO METHANOL H-BONDING BETWEEN TWO METHANOL MOLECULESMOLECULES
H-bondH-bondH-bondH-bond
--++
--
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HYDROGEN BONDING IN HHYDROGEN BONDING IN H22OOHYDROGEN BONDING IN HHYDROGEN BONDING IN H22OO
H-bonding is H-bonding is especially strong in especially strong in water becausewater because
the O—H bond is the O—H bond is very polarvery polar
there are 2 lone there are 2 lone pairs on the O atompairs on the O atom
Accounts for many of Accounts for many of water’s unique water’s unique properties.properties.http://www.visionlearning.com/library/flash_viewer.php?
oid=1435&mid=120Animation of Ice
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HYDROGEN BONDING IN HHYDROGEN BONDING IN H22OOHYDROGEN BONDING IN HHYDROGEN BONDING IN H22OO
Ice has open Ice has open lattice-like lattice-like structure.structure.
Ice density is Ice density is < liquid.< liquid.
And so solid And so solid floats on floats on water.water.
Snow flake: www.snowcrystals.com
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HYDROGEN BONDING IN HHYDROGEN BONDING IN H22OOHYDROGEN BONDING IN HHYDROGEN BONDING IN H22OO
Ice has open lattice-like structure.Ice has open lattice-like structure.
Ice density is < liquid and so solid floats on Ice density is < liquid and so solid floats on water.water.
One of the VERY few substances One of the VERY few substances where solid is LESS DENSE than where solid is LESS DENSE than the liquid.the liquid.
http://www.visionlearning.com/library/flash_viewer.php?oid=1380&mid=57H bonding in Water
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HYDROGEN BONDINGHYDROGEN BONDINGHYDROGEN BONDINGHYDROGEN BONDING
H bonds leads to H bonds leads to abnormally high abnormally high boiling point of water.boiling point of water.
See Screen 13.7See Screen 13.7
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BOILING POINTS OF SIMPLE BOILING POINTS OF SIMPLE HYDROGEN-CONTAINING HYDROGEN-CONTAINING COMPOUNDSCOMPOUNDS
See Active Figure 12.8See Active Figure 12.8
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METHANE HYDRATEMETHANE HYDRATEMETHANE HYDRATEMETHANE HYDRATE
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HYDROGEN BONDING IN HYDROGEN BONDING IN BIOLOGYBIOLOGYHYDROGEN BONDING IN HYDROGEN BONDING IN BIOLOGYBIOLOGY
H-bonding is especially strong in H-bonding is especially strong in biological systems — such as DNA. biological systems — such as DNA.
DNA — helical chains of phosphate DNA — helical chains of phosphate groups and sugar molecules. Chains are groups and sugar molecules. Chains are helical because of tetrahedral geometry helical because of tetrahedral geometry of P, C, and O.of P, C, and O.
Chains bind to one another by specific Chains bind to one another by specific hydrogen bonding between pairs of hydrogen bonding between pairs of Lewis bases.Lewis bases.
——adenine with thymineadenine with thymine ——guanine with cytosineguanine with cytosine
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Portion of a DNA Portion of a DNA chainchain
Double helix of Double helix of DNADNA
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BASE-PAIRING THROUGH H-BONDSBASE-PAIRING THROUGH H-BONDSBASE-PAIRING THROUGH H-BONDSBASE-PAIRING THROUGH H-BONDS
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HYDROGEN BONDING IN HYDROGEN BONDING IN BIOLOGYBIOLOGYHYDROGEN BONDING IN HYDROGEN BONDING IN BIOLOGYBIOLOGY
Hydrogen bonding and base pairing in DNA.Hydrogen bonding and base pairing in DNA.
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H BONDING ACTIVITY
With your elbow partner, draw the following on the same sheet of paper taking turns:
1. Water Molecule2. Dipole of this water molecule3. Another water molecule4. Hydrogen Bonding Between these molecules5. Structure of Ice6. Reflect on your beautiful drawings and give
each other high fives.
30
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* There is no strict cutoff for the ability to form H-bonds (S forms a biologically important hydrogen bond in proteins).
* Hold DNA strands together in double-helix
31Nucleotide pairs form H-
bonds DNA double helix
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2. INDUCTIVE FORCES: Arise from distortion of the e- cloud induced by the
electrical field produced by another particle or molecule nearby.
London dispersion: between polar or nonpolar molecules or atoms * Proposed by Fritz London in 1930 Must exist because nonpolar molecules form liquids
32
Fritz London(1900-1954)
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How they form:1. Motion of e- creates an instantaneous dipole moment,
making it “temporarily polar”.
33
2. Instantaneous dipole moment induces a dipole in an adjacent atom
• * Persist for about 10-14 or 10-15 second
Ex: two He atoms
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
How can non-polar molecules such as OHow can non-polar molecules such as O2 2 and Iand I22 dissolve in dissolve in water?water?
The water dipole The water dipole INDUCESINDUCES a dipole in the O a dipole in the O22 electric electric cloud. cloud.
Dipole-induced dipoleDipole-induced dipoleDipole-induced dipoleDipole-induced dipole
http://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtmlDipole-Dipole and LDFs
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Solubility increases with mass the gasSolubility increases with mass the gas
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Process of inducing Process of inducing a dipole is a dipole is polarizationpolarization
Degree to which Degree to which electron cloud of an electron cloud of an atom or molecule atom or molecule can be distorted in can be distorted in its its polarizabilitypolarizability..
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IM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLESIM FORCES — INDUCED DIPOLES
Consider IConsider I22 dissolving dissolving in ethanol, in ethanol, CHCH33CHCH22OH.OH.
OH
-
+
I-I
R
-
+
OH
+
-
I-I
R
The alcohol The alcohol temporarily temporarily creates or creates or
INDUCESINDUCES a dipole a dipole in Iin I22..
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Formation of a dipole in two nonpolar IFormation of a dipole in two nonpolar I22 molecules. molecules.
Induced dipole-induced Induced dipole-induced dipoledipoleInduced dipole-induced Induced dipole-induced dipoledipole
http://chemmovies.unl.edu/ChemAnime/LONDOND/LONDOND.htmlLDFs
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FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
The induced forces between IThe induced forces between I22 molecules are molecules are
very weak, so solid Ivery weak, so solid I22 sublimessublimes (goes (goes from a solid to gaseous molecules).from a solid to gaseous molecules).
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INTERMOLECULAR FORCESINTERMOLECULAR FORCES
See Figure 12.12See Figure 12.12
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LIQUIDSLIQUIDSSECTION 12.4SECTION 12.4
LIQUIDSLIQUIDSSECTION 12.4SECTION 12.4
In a liquidIn a liquid•• molecules are in molecules are in
constant motionconstant motion•• there are appreciable there are appreciable
intermolec. forcesintermolec. forces•• molecules close molecules close
togethertogether•• Liquids are almost Liquids are almost
incompressibleincompressible•• Liquids do not fill the Liquids do not fill the
containercontainer
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LIQUIDSLIQUIDSThe two key properties we need to The two key properties we need to
describe are describe are EVAPORATIONEVAPORATION and its and its opposite—opposite—CONDENSATIONCONDENSATION
The two key properties we need to The two key properties we need to describe are describe are EVAPORATIONEVAPORATION and its and its opposite—opposite—CONDENSATIONCONDENSATION
break IM bonds
make IM bonds
Add energy
Remove energy
LIQUID VAPOR
r r condensationcondensation
Evaporation Evaporation ff
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LIQUIDS—EVAPORATIONLIQUIDS—EVAPORATIONTo evaporate, molecules To evaporate, molecules
must have sufficient must have sufficient energy to break IM energy to break IM forces.forces.
Breaking IM forces requires Breaking IM forces requires energy. The process of energy. The process of evaporation is evaporation is endothermicendothermic..
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LIQUIDS—LIQUIDS—DISTRIBUTION OF ENERGIESDISTRIBUTION OF ENERGIES
Distribution of Distribution of molecular molecular energies in a energies in a liquid.liquid.
KE is propor-KE is propor-tional to T.tional to T.
Distribution of Distribution of molecular molecular energies in a energies in a liquid.liquid.
KE is propor-KE is propor-tional to T.tional to T.
0
Number of molecules
Molecular energy
higher Tlower T
See Figure 12.13See Figure 12.13
Minimum energy req’d to break IM forces and evaporate
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VAPOR PRESSUREVAPOR PRESSURE
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EQUILIBRIUM VAPOR PRESSUREEQUILIBRIUM VAPOR PRESSURE
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swfVapor Pressure
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LIQUIDSLIQUIDSHEAT OF VAPORIZATIONHEAT OF VAPORIZATION is the heat req’d (at is the heat req’d (at
constant P) to vaporize the liquid.constant P) to vaporize the liquid.
LIQ + heat LIQ + heat ff VAP VAP
Compd.Compd. ∆∆vapvapH (kJ/mol) H (kJ/mol) IM ForceIM Force
HH22OO 40.7 (100 40.7 (100 ooC)C) H-bondsH-bonds
SOSO22 26.8 (-47 26.8 (-47 ooC)C) dipoledipole
XeXe 12.6 (-107 12.6 (-107 ooC)C) induced induced dipole dipole
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EQUILIBRIUM VAPOR PRESSURE & THE EQUILIBRIUM VAPOR PRESSURE & THE CLAUSIUS-CLAPEYRON EQUATIONCLAUSIUS-CLAPEYRON EQUATION
Clausius-Clapeyron equation — Clausius-Clapeyron equation —
used to find ∆used to find ∆vapvapH˚.H˚.
The logarithm of the vapor The logarithm of the vapor
pressure P is proportional to pressure P is proportional to
∆∆vapvapH and to 1/T.H and to 1/T.
ln P = –(∆ln P = –(∆vapvapH˚/RT) + CH˚/RT) + C
ln P2
P1
= ĘvapH
R
1
T1
- 1
T2
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SURFACE TENSIONSURFACE TENSION
SURFACE TENSIONSURFACE TENSION also leads to also leads to spherical liquid droplets.spherical liquid droplets.
SURFACE TENSIONSURFACE TENSION also leads to also leads to spherical liquid droplets.spherical liquid droplets.
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11.3: PROPERTIES RESULTING FROM IMF
1. Viscosity: resistance of a liquid to flow
2. Surface tension: energy required to increase the surface area of a liquid
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LIQUIDSLIQUIDSIntermolec. forces also lead to Intermolec. forces also lead to CAPILLARYCAPILLARY
action and to the existence of a concave action and to the existence of a concave meniscus for a water column.meniscus for a water column.
concavemeniscus
H2O in
glasstube
ADHESIVE FORCESbetween waterand glass
COHESIVE FORCESbetween watermolecules
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CAPILLARY ACTIONCAPILLARY ACTION
Movement of water up a piece of Movement of water up a piece of paper depends on H-bonds between paper depends on H-bonds between HH22O and the OH groups of the O and the OH groups of the cellulose in the paper.cellulose in the paper.
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3. Cohesion: attraction of molecules for other molecules of the same compound
4. Adhesion: attraction of molecules for a surface
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5. Meniscus: curved upper surface of a liquid in a container; a relative measure of adhesive and cohesive forcesEx:
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Hg H2O(cohesion rules) (adhesion rules)
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* GECKOS!
Geckos’ feet make use of London dispersion forces to climb almost anything. A gecko can hang on a glass
surface using only one toe.
Researchers at Stanford University recently developed a gecko-like robot which uses synthetic setae to climb walls
http://www.visionlearning.com/library/module_viewer.php?mid=57
Jesus Lizard
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http://en.wikipedia.org/wiki/Van_der_Waals%27_force
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London dispersion forces (induced dipole-induced dipole) increase with:
Increasing MW, # of e-, and # of atoms (increasing # of e- orbitals to be distorted)Boiling points:
Effect of MW: Effect of # atoms:pentane 36ºC Ne –246°C hexane 69ºC CH4 –162°Cheptane 98ºC
??? effect:H2O 100°CD2O 101.4°C
“Longer” shapes (more likely to interact with other molecules)
C5H12 isomers: 2,2-dimethylpropane 10°C pentane
36°C56
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SUMMARY OF IMF
Van der Waals forces
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Ex: Identify all IMF present in a pure sample of each substance, then explain the boiling points.
BP(⁰C)
IMF Explanation
HF 20
HCl -85
HBr -67
HI -35
Lowest MW/weakest London, but most
polar/strongest dipole-dipole and has H-bonds
Low MW/weak London, moderate polarity/dipole-
dipole and no H-bonds
Medium MW/medium London, moderate
polarity/dipole-dipole and no H-bonds
Highest MW/strongest London, but least polar bond/weakest dipole-dipole and no H-bonds
London, dipole-dipole, H-bonds
London, dipole-dipole
London, dipole-dipole
London, dipole-dipole
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11.4: PHASE CHANGES
Processes: Endothermic: melting,
vaporization, sublimation Exothermic: condensation,
freezing, deposition
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I2 (s) and (g)
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WATER: ENTHALPY DIAGRAM OR HEATING CURVE
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J/g) 334(mQ
TmQ )CJ/g 4.18(
TmQ )CJ/g 87.1(
TmQ )CJ/g 06.2(
J/g) 2602(mQ
TmcQ
mHQ
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GROUP ACTIVITY
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Get in groups of four.Two people will need to draw and two will need to explainChoose roles.First drawer draws a phase diagram of water.Second drawer draws a phase diagram of CO2Third member explains the water’s phase diagramFourth member explains CO2’s phase diagram.
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11.7-8: STRUCTURES OF SOLIDS
Amorphous: without orderly structureEx: rubber, glass
Crystalline: repeating structure; have many different stacking patterns based on chemical formula, atomic or ionic sizes, and bonding
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TYPES OF CRYSTALLINE SOLIDS (TABLE 11.6)
Type Particles ForcesNotable
propertiesExample
s
Atomic AtomsLondon
dispersion
Poor conductors
Very low MP
Ar (s),Kr (s)
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Molecular
Molecules
(polar or non-
polar)
London dispersion, dipole-
dipole, H-bonds
Poor conductors
Low to moderate MP
CO2 (s),
C12H22O11,
H2O (s)
SucroseCarbon dioxide (dry ice)
Ice
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Ionic
Anions and
cations
Electrostatic attractions
Hard & brittle
High MPPoor conductors
Some solubility in H2O
NaCl,Ca(NO3)2
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Covalent (a.k.a.
covalent network)
Atoms bonded
in a covalent network
Covalent bonds
Very hardVery high MP
Generally insoluble
Variable conductivity
C (diamond
& graphite)
SiO2
(quartz)
Ge, Si, SiC, BN
DiamondGraphite SiO2
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Metallic
Metal cations in a diffuse, delocalized e- cloud
Metallic bonds
Excellent conductors
MalleableDuctileHigh but wide range of MP
Cu, Al, Fe