Ch 11: Intermolecular Forces and Types of Solids Brown, LeMay AP Chemistry Monta Vista High School.
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Transcript of Ch 11: Intermolecular Forces and Types of Solids Brown, LeMay AP Chemistry Monta Vista High School.
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.
311.1: 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.
Summary of Intermolecular Summary of Intermolecular ForcesForcesSummary of Intermolecular Summary of Intermolecular ForcesForces
• Ion-Ion forcesIon-Ion forces• Ion-dipole forcesIon-dipole forces•Dipole-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)
611.2: Types of IMF1. 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)
2d
QQF
http://chemmovies.unl.edu/ChemAnime/IONSIZED/IONSIZED.html Ion size and LE
7b. Ion-dipole: between an ion and a dipole (a neutral, polar molecule/has separated partial charges) 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
Attraction Between Attraction Between Ions and Permanent Ions and Permanent DipolesDipoles
Attraction Between Attraction Between Ions and Permanent Ions and Permanent DipolesDipoles
Water is highly polar Water is highly polar and can interact and can interact with positive ions to with positive ions to
give give hydratedhydrated ions in water.ions in water.
HH
water dipole
••
••
O-
+
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+
Attraction Between Attraction Between Ions and Permanent Ions and Permanent DipolesDipoles
Attraction Between Attraction Between Ions and Permanent Ions and Permanent DipolesDipoles
10c. Dipole-dipole: weakest electrostatic force (Not all IMFs, LDFs weaker than dipole-dipole); exist between neutral polar molecules Increase with increasing
polarity (dipole moment) of molecule
Ex: What IMF exist in NaCl (aq)?
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
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
13
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
14
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:
F-H
O-H
N-H
:F
:O
:N
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
16 H-bonds explain why ice is less dense than water.
http://en.wikipedia.org/wiki/Water_%28molecule%29#Density_of_water_and_ice
17
Ex: Boiling points of nonmetal hydrides
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
H-Bonding Between H-Bonding Between Methanol and WaterMethanol and WaterH-Bonding Between H-Bonding Between Methanol and WaterMethanol and Water
H-bondH-bondH-bondH-bond--
++
--
H-Bonding Between Two H-Bonding Between Two Methanol MoleculesMethanol MoleculesH-Bonding Between Two H-Bonding Between Two Methanol MoleculesMethanol Molecules
H-bondH-bondH-bondH-bond
--++
--
Hydrogen Bonding in HHydrogen Bonding in H22OOHydrogen Bonding in HHydrogen Bonding in H22OO
H-bonding is especially H-bonding is especially strong in water strong in water becausebecause
• the O—H bond is the O—H bond is very polarvery polar
• there are 2 lone pairs there are 2 lone pairs on the O atomon 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
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
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 One of the VERY few substances where solid is substances where solid is LESS DENSE than the LESS DENSE than the liquid.liquid.
http://www.visionlearning.com/library/flash_viewer.php?oid=1380&mid=57H bonding in Water
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
PLAY MOVIE
Boiling Points of Boiling Points of Simple Hydrogen-Simple Hydrogen-Containing Containing CompoundsCompounds
See Active Figure 12.8See Active Figure 12.8
Hydrogen Bonding in Hydrogen Bonding in BiologyBiologyHydrogen Bonding in Hydrogen Bonding in BiologyBiology
H-bonding is especially strong in biological H-bonding is especially strong in biological systems — such as DNA. systems — such as DNA.
DNA — helical chains of phosphate groups DNA — helical chains of phosphate groups and sugar molecules. Chains are helical and sugar molecules. Chains are helical because of tetrahedral geometry of P, C, because of tetrahedral geometry of P, C, and O.and O.
Chains bind to one another by specific Chains bind to one another by specific hydrogen bonding between pairs of Lewis hydrogen bonding between pairs of Lewis bases.bases.
——adenine with thymineadenine with thymine
——guanine with cytosineguanine with cytosine
Base-Pairing through H-BondsBase-Pairing through H-BondsBase-Pairing through H-BondsBase-Pairing through H-Bonds
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.
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
31 * 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
Nucleotide pairs form H-bonds
DNA double helix
322. 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
Fritz London(1900-1954)
33How they form:1. Motion of e- creates an instantaneous
dipole moment, making it “temporarily polar”.
2. Instantaneous dipole moment induces a dipole in an adjacent atom• * Persist for about 10-14 or 10-15 second
Ex: two He atoms
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESHow can non-polar molecules such as OHow can non-polar molecules such as O2 2 and Iand I22 dissolve in water? dissolve in water?
The water dipole The water dipole INDUCESINDUCES a dipole in a dipole in the Othe O22 electric cloud. electric cloud.
Dipole-induced Dipole-induced dipoledipole
Dipole-induced Dipole-induced dipoledipole
http://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtmlDipole-Dipole and LDFs
FORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLESFORCES INVOLVING FORCES INVOLVING INDUCED DIPOLESINDUCED DIPOLES
Solubility increases with mass the gasSolubility increases with mass the gas
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..
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 a dipole in Idipole in I22..
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 dipole-induced dipoleinduced dipoleInduced dipole-Induced dipole-induced dipoleinduced dipole
http://chemmovies.unl.edu/ChemAnime/LONDOND/LONDOND.htmlLDFs
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).
PLAY MOVIE
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
PLAY MOVIE
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
Liquids—Liquids—EvaporationEvaporation
To evaporate, molecules To evaporate, molecules must have sufficient must have sufficient energy to break IM forces.energy to break IM forces.
Breaking IM forces Breaking IM forces requires energy. The requires energy. The process of evaporation process of evaporation is is endothermicendothermic..
Liquids—Liquids—Distribution of EnergiesDistribution of Energies
Distribution of Distribution of molecular molecular energies in energies in a liquid.a liquid.
KE is propor-KE is propor-tional to T.tional to T.
Distribution of Distribution of molecular molecular energies in energies in a liquid.a liquid.
KE is propor-KE is propor-tional to T.tional to T.
0
Num
ber
of m
olec
ules
Molecular energy
higher Tlower T
See Figure 12.13See Figure 12.13
Minimum energy req’d to break IM forces and evaporate
Equilibrium Vapor PressureEquilibrium Vapor Pressure
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swfVapor Pressure
LiquidsLiquidsHEAT OF VAPORIZATIONHEAT OF VAPORIZATION is the heat is the heat
req’d (at constant P) to vaporize the liquid.req’d (at 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
Equilibrium Vapor Pressure & Equilibrium Vapor Pressure & the Clausius-Clapeyron Equationthe Clausius-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
Surface TensionSurface Tension
SURFACE TENSIONSURFACE TENSION also leads to spherical also leads to spherical liquid droplets.liquid droplets.
SURFACE TENSIONSURFACE TENSION also leads to spherical also leads to spherical liquid droplets.liquid droplets.
5111.3: 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
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
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.
PLAY MOVIE
543. Cohesion: attraction of molecules for other molecules of the same compound
4. Adhesion: attraction of molecules for a surface
55
5. Meniscus: curved upper surface of a liquid in a container; a relative measure of adhesive and cohesive forcesEx:
Hg H2O(cohesion rules) (adhesion rules)
56* 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=57Jesus Lizard
http://en.wikipedia.org/wiki/Van_der_Waals%27_force
57London 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°C
D2O 101.4°C
“Longer” shapes (more likely to interact with other molecules)
C5H12 isomers: 2,2-dimethylpropane 10°C pentane
36°C
59Ex: 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
6011.4: Phase ChangesProcesses: Endothermic: melting,
vaporization, sublimation Exothermic:
condensation, freezing, deposition
I2 (s) and (g)
Microchip
61Water: Enthalpy diagram or heating curve
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
6211.5: Vapor pressure
A liquid will boil when the vapor pressure equals the atmospheric pressure, at any T above the triple point.
Pressure cooker ≈ 2 atm
Normal BP = 1 atm
10,000’ elev ≈ 0.7 atm
29,029’ elev (Mt. Everest) ≈ 0.3 atm
6311.6: Phase diagrams: CO2
Lines: 2 phases exist in equilibrium
Triple point: all 3 phases exist together in equilibrium (X on graph)
Critical point, or critical temperature & pressure: highest T and P at which a liquid can exist (Z on graph)
For most substances, inc P will cause a gas to condense (or deposit), a liquid to freeze, and a solid to become more dense (to a limit.)
Temp (ºC)
Group Activity 67
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.
6811.7-8: 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
Types of crystalline solids (Table 11.6)
Type Particles ForcesNotable
propertiesExample
s
Atomic AtomsLondon
dispersion
Poor conductors
Very low MP
Ar (s),Kr (s)
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
Ionic
Anions and
cations
Electrostatic attractions
Hard & brittle
High MPPoor conductors
Some solubility in H2O
NaCl,Ca(NO3)2
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