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Chapter 10

Lecture Notes for General Chemistry

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
1.36 L atm / mol
Water is polar and shows more electron density (red) on O-atom
Oxygen is more electronegative than Hydrogen
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:
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
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
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
surface tension
capillary action
energy needed to separate the molecules of unit area on the surface of a liquid
reason cold needle floats on surface of
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
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
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
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?
What do we know?
T = 0 + 273.15 = 273.15 K P = 250 torr
T = 373.15 K P = 500 torr
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
cubic array of tightly packed atoms or molecules
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
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
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
Molecular Orbital Theory for Metals
Quick Review of MOT
Applied to Metals
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
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

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
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