ch 10: intermolecular forces and types of solids
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Ch 10: Intermolecular Forces and Types of Solids. AP Chemistry Sequoyah High School. 10.1: Intermolecular Forces (IMF). IMF < intramolecular forces (covalent, metallic, ionic bonds) IMF strength: solids > liquids > gases - PowerPoint PPT PresentationTRANSCRIPT
210.1: 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.
310.1: Types of IMF1. Electrostatic forces: act over larger
distances in accordance with Coulomb’s law
http://dwb4.unl.edu/ChemAnime/attractive_forces.htm
a.Ion-ion forces: strongest; found in ionic crystals (i.e. lattice energy)
http://chemmovies.unl.edu/ChemAnime/LICLD/LICLD.html
2d
QQF
4b. 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://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_14/Dissolution_NaCl_Water.MO
5c. Dipole-dipole: weakest electrostatic force; exist between neutral polar molecules Increase with increasing
polarity (dipole moment) of molecule
Ex: What IMF exist in NaCl (aq)?http://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml
http://usm.maine.edu/~newton/Chy251_253/Lectures/CarbonylReduction/AldehydesKetones.html
6
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.visionlearning.com/library/module_viewer.php?mid=57
( ice and water simulation)http://www.youtube.com/watch?v=LGwyBeuVjhU ( H bond
movie)http://www.youtube.com/watch?
v=lkl5cbfqFRM&feature=related ( H bonding in water)
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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:
F-H
O-H
N-H
:F
:O
:N
8 * 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
9 H-bonds explain why ice is less dense than water.
http://www.youtube.com/watch?v=PcoiLAsUvqc&feature=related http://www.youtube.com/watch?v=gmjLXrMaFTg&feature=relatedhttp://en.wikipedia.org/wiki/Water_%28molecule%29#Density_of_water_and_ice
10
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
112. 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)
12How 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
http://dwb4.unl.edu/ChemAnime/LONDOND/LONDOND.html
Ex: two He atoms
13* 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://en.wikipedia.org/wiki/Van_der_Waals%27_force
14London dispersion forces 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
16Ex: 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
1710.2: 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
183. 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:
Hg H2O(cohesion rules) (adhesion rules)
2010.8: Phase ChangesProcesses: Endothermic: melting,
vaporization, sublimation Exothermic:
condensation, freezing, deposition
I2 (s) and (g)
Microchip
21Water: 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
2210.8: Vapor pressure
A liquid will boil when the vapor pressure equals the atmospheric pressure, at any T above the triple point.
http://glencoe.com/sites/common_assets/advanced_placement/chemistry_chang9e/animations/chang_2e/vapor_pressure.swfhttp://dwb4.unl.edu/ChemAnime/VPTEMPD/VPTEMPD.htmlhttp://dwb4.unl.edu/ChemAnime/VP3LIQD/VP3LIQD.html
Pressure cooker ≈ 2 atm
Normal BP = 1 atm
10,000’ elev ≈ 0.7 atm
29,029’ elev (Mt. Everest) ≈ 0.3 atm
2310.9: 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)
2710.3-7: 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