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Chapter 10

Lecture Notes for General Chemistry
by

Aimee Tomlinson

on 24 June 2014

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Transcript of Chapter 10

Chapter 10: Liquids & Solids
10.1: Polar Covalent Bonds & Dipole Moments
10.2: Intermolecular Forces
10.3: Some Properties of Liquids
10.4 & 10.5: Phase Changes, Evaporation, Vapor Pressures & Boiling Points
10.6: Kinds of Solids
10.7 - 10.10: SKIP!!!
21.4 - 21.5: Bonding in Metals & Semiconductors
10.11: Phase Diagrams
van der Waals gas Constants
5.28 L atm / mol
2
2
1.36 L atm / mol
2
2
Water is polar and shows more electron density (red) on O-atom
Oxygen is more electronegative than Hydrogen
http://www.bpreid.com/3_bonding.php
Therefore, there are electrostatic interactions between water molecules
NOTE: Oxygen gas does not have a non-zero constant - we will talk about this later
polar bonds & polar molecules
bond dipole
change in EN between 2 atoms makes the bond connecting them polar
this phenomenon leads to a bond dipole:
less EN atom (+)
more EN atom (-)
permanent dipole moment
when a molecule possesses asymmetry then it will have a permanent dipole:
NH , H O, SO , SF , XeOF
molecules that have a zero dipole moment (0 Debye) possess symmetry:
NH , CBr , BF, BeCl , PCl , I , SF , XeF
more examples of symmetry & dipole moments:
3
2
2
4
4
4
+
4
3
2
5
3
-
6
4
dipole-dipole
polarizability
London dispersion
between molecules NOT within a single molecule
"dipole" since the molecule has a nonzero DPM
less EN element is (+) while the more EN element is (-)
thereby generating a "pole"
the more cationic the atom the less EN and vice-versa
generated as a consequence of the lone pairs of the very EN atom
and their interaction with hydrogen
leads to a number of interesting properties:
- high boiling point of water
- formation of the double helix in DNA
most powerful dipole-dipole
occurs between a molecule possessing an H-atom and an adjacent molecule possessing either O, N, F
hydrogen bonding
So far ...
H-bonding > dipole-dipole
ion-dipole
O --- Na
+
H --- Cl
-
attractive forces occur between oppositely charged species
very strong interaction leads to a larger vdW constant
the more polar the molecule the stronger the ion-dipole interaction
Now we have ...
ion-dipole > H-bonding > dipole-dipole
Why does O have a nonzero van der Waals constant?
It is due to polarizability: the distortion of the electron cloud around
the atom's nucleus as another atom or molecule approaches
results from electron-electron repulsion
the larger the cloud the more polarizable the species
think big spongy nerf ball versus very hard smaller baseball
Ar: 3.59 L atm/mol
He: 0.0341 L atm/mol
2
2
2
2
So, what does this mean with respect to our intermolecular forces?
the more polarizable a species the larger its induced dipole
distortion of the electron cloud causing a temporary dipole by partially
exposing the nucleus
this then leads to what is called induced dipole - induced dipole the weakest
of the forces
other names for this force: van der Waals, London dispesion or disperson
this is the only force which occurs between non-polar species - however, it is
present in all intermolecular interactions
Finally we have ...
ion-dipole > H-bonding > dipole-dipole > dipole - induced dipole > induced dipole - induced dipole
http://butane.chem.uiuc.edu
surface tension
meniscus
capillary action
viscosity
http://commons.wikimedia.org/wiki/File.Aguja_tens_sup.jpg
www.photoshelter.com/image/10000PEyxG9NfTYA
www.candle-licious.com/page/C/PROD/Flameless/ReedDiffuser
syntheticlubricants.ca/Pics/viscosity.gif
energy needed to separate the molecules of unit area on the surface of a liquid
reason cold needle floats on surface of
water
hot needle will sink
surface tension of water is a
consequence of H-bond
curved surface of a liqud as a result of forces
cohesive: forces between same type of molecule (e.g. H-bonds in water)
adhesive: forces between different species (e.g. dipole-dipole of water with glass)
rise of the liquid up a narrow tube - result of cohesive & adhesive forces
cohesive forces between liquid molecules
adhesive forces between liquid and tube molecules
e.g. way trees and plants obtain water from the soil
resistance of a liquid to flow
molasses is very viscous whereas
water is not
heating will lower a fluids' viscosity
since it will weaken intermolecular
forces
result of molecules escaping from liquid to gas
process: vaporization/evaporation
endothermic since energy/heat must be added
to break the intermolecular bonds between liquid
molecules
opposite process: condensation
exothermic since gas molecules are cooled in order
to condense back to liquid
amount: heat of vaporization
defn: energy required to vaporize 1 mole of liquid at
a pressure of 1 atm
measuring the heat of vaporization
vapor pressure
www.instablogsimages.com/images/2010/03/02/ha..
if we have a list of vapor pressures at different temperatures:


if we are given two temperatures:
What is the heat of vaporization of X if the vapor pressure
at 0 C is 250 torr and the vapor pressure at 100 C is 500 torr?
o
o
What do we know?
T = 0 + 273.15 = 273.15 K P = 250 torr
2
1
T = 373.15 K P = 500 torr
2
1
What relationships do we know?
What do we want know?
other changes of state
sublimation: endothermic process s -> g
solidification: exothermic process g -> s or l -> s
melting: endothermic process: s -> l
all of these processes have an accompanying enthalpy
Final Note: to change a state we must overcome
the intermolecular forces holding that state together
http://www.ice-agency.com/ice-dry-ice/p-dryice.jpeg
www.flickr.com/photos/pa-i_ki-i/2494130750/
cubic array of tightly packed atoms or molecules
http://www.personal.kent.edu/~cearley/ChemWrld/jmol/crystals/NaCl3d.png
commons.wikimedia.org/wiki/File:Hex_ice.GIF
Copyright Oliver Kreylos, Center for Image Processing and Integrated Computing (CIPIC), University of California, Davis.
Crystalline Solids
ionic solids
comprised of anions & cations
atomic solids
comprised of a single atom
molecular solids
comprised of a single molecule
Amorphous Solids
completely unstructured
Structure & Bonding in Metals
lattice: refers to the 3D array of particles in a crystalline solid
unit cell: basic repeating unit of the particle arrangement in a crystalline solid
arrangement types
simple cubic
body-centered
cubic
face-centered
cubic
http://explorepdx.com/oneshot.jpg
8 corner pieces
each corner piece is worth 1/8
8 (1/8) = 1
Therefore, 1 atom/ion is present in this structure
8 corner pieces + 1 body piece
each body piece is worth 1
8 (1/8) +1 = 2
Therefore, 2 atom/ion(s) is present in this structure
www.meatfighter.com/puls/
8 corner + 6 face pieces
each face piece is worth 1/2
8 (1/8) + 6(1/2) = 4
Therefore, 4 atom/ion(s) is present in this structure
http://matdl.org/repository/eserv/matdl:829/web_wiki2fez2437.jpg
Molecular Orbital Theory for Metals
Semiconductors
Quick Review of MOT
Applied to Metals
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch02/ans2-3-4.jpg
atomic orbitals (AOs) combine in two ways:
- constructively to form bonding molecular orbitals (MOs)
- destructively to form antibonding molecular orbitals
AOs in = MOs out
as we increase the number of Na atoms we increase the number of AOs
and hence the number of MOs generated
eventually two bands will be formed
- lower band (aka valence band) is comprised of bonding MOs
- upper band (aka conduction band) is comprised of antibonding MOs
Ways to increase semiconductor conductivity:
increase T
– the opposite occurs for metals (structure begins to break – melting begins)
add impurities aka dopants
– because we increase the number of charge carriers
Types of semiconductors:
n-type semiconductor (‘n’ = negative)
– adding a dopants with more electrons (adding P to a silicon network)
– the leftover electron is the charge carrier
p-type semiconductor (‘p’ = positive)
– adding a dopants with less electrons (adding B to a silicon network)
– the leftover hole is the charge carrier
typically all metals are conductors
all nonmetals are insulators
metalloids are semiconductors
Conductivity & Elemental Type
Intermolecular Forces & Phases
intermolecular force strength, T and P contribute to the phase
at lower T and P gases are preferred
solids are more likely at higher P and lower T
www.sciforums.com/showthread.php?p=2060322
bhs.smuhsd.org/.../apchemistry/h2ophase.gif
graphical representation of the physical states as a function of T&P
melting point line (s & l)
boiling point line (l & g)
sublimation point line (s & g)
Carbon Dioxide - An Example
lines in diagram
triple point (s, l & g)
critical point (l & g)
- g & l phases are indistinguishable
fluid phase: density is the same for both
- used in the decaffeination process
normal points:
- boiling point T at 1 atm
- freezing point T at 1 atm
unique to water:
- negative slope of mpt line due to H-bonds
- downward slope of spt line - why ice melts
in freezer
points in diagram
Water - Another Example

4
Non polar molecules
have the same molecular & electronic geometries
possess no lone pairs about the central atom
are completely symmetric
may possess polar bonds (e.g. CCl )
only experience dispersion forces (induced-dipole)
Polar molecules
have the different molecular & electronic geometries (unless the molecule is linear)
may possess lone pairs about the central atom
are not completely symmetric
possess polar bonds
experience at least dipole-dipole interactions
Full transcript