Polonium-210 Poisoning
#atoms Po210 = (1.0mgPo210Cl2)(1g/106mg)
(6.02x1023atoms/mol)(1mol/280gPoCl2)
= 2.2x1015 atoms
t1/2 = 138 days by a decay of 5.3MeV energy
10a few hundred atoms Po-110 per cell
Even if only 10% decay, 110 decays per cell
Former Russian spy died 22 days after the poisoning
incident.
The Po210 would decay by a little more than 10% in
22 days.
Chemical & Engineering News, Dec. 4, 2006 pg.15
Dr. S. M. Condren
Chapter 13
Intermolecular Forces:
Liquids, and Solids
Dr. S. M. Condren
WHY?
• Why is water usually a liquid
and not a gas?
• Why does liquid water boil at
such a high temperature for
such a small molecule?
• Why does ice float on water?
• Why do snowflakes have 6
sides?
• Why is I2 a solid whereas Cl2
is a gas?
• Why are NaCl crystals little
cubes?
Dr. S. M. Condren
Inter-molecular Forces
Have studied INTRAmolecular forces
— the forces holding atoms together to form
molecules.
Now turn to forces between molecules
— INTERmolecular forces.
Forces between molecules/atoms, between
ions, or between molecules/atoms and ions.
Dr. S. M. Condren
Dr. S. M. Condren
Ion-Ion Forces for
comparison of magnitude
Na+—Cl- in salt
These are the
strongest forces.
Lead to solids with
high melting
temperatures.
NaCl, mp = 800 oC
MgO, mp = 2800 oC
Dr. S. M. Condren
Covalent Bonding Forces
for comparison of magnitude
C=C, 610 kJ/mol
C–C, 346 kJ/mol
C–H, 413 kJ/mol
CN, 887 kJ/mol
Dr. S. M. Condren
Attraction Between Ions
and Permanent Dipoles
••
••
water
-
dipole
O
H
H +
Water is highly polar and
can interact with positive
and negative ions to give
hydrated ions in water.
Dr. S. M. Condren
Attraction Between Ions
and Permanent Dipoles
Many metal ions are hydrated.
This is the reason metal salts
dissolve in water.
Dr. S. M. Condren
Attraction Between Ions
and Permanent Dipoles
Attraction between ions and dipole depends
on ion charge and ion-dipole distance.
Measured by ∆H for
Mn+ + xH2O --> [M(H2O)x]n+
- H
O
H
+
•••
Mg2+
- H
O
H
+
- H
O
H
+
•••
Na +
-1922 kJ/mol -405 kJ/mol
Dr. S. M. Condren
•••
Cs+
-263 kJ/mol
Dipole-Dipole Forces
Such forces bind molecules
having permanent dipoles to one
another.
Dr. S. M. Condren
Dipole-Dipole Forces
Influence of dipole-dipole forces is seen
in the boiling points of simple
molecules.
Comp’d
Mol. Wt.
Boil Point
N2
28
-196 oC
CO
28
-192 oC
Br2
160
59 oC
ICl
162
97 oC
Dr. S. M. Condren
Hydrogen Bonding
A special form of dipole-dipole
attraction, which enhances dipoledipole attractions.
H-bonding is strongest when X and Y are N, O, or F
Dr. S. M. Condren
H-Bonding Between
Methanol and Water
-
H-bond
+
-
Dr. S. M. Condren
H-Bonding Between
Two Methanol Molecules
-
+
-
H-bond
Dr. S. M. Condren
H-Bonding Between
Ammonia and Water
-
+
-
H-bond
This H-bond leads to the formation of
NH4+ and OH- Dr. S. M. Condren
Hydrogen Bonding in H2O
H-bonding is
especially strong in
water because
• the O—H bond is
very polar
• there are 2 lone
pairs on the O atom
Accounts for many of
water’s unique
properties.
Dr. S. M. Condren
Hydrogen Bonding in H2O
Ice has open
lattice-like
structure.
Ice density is
< liquid.
And so solid
floats on
water.
Dr. S. M. Condren
Hydrogen Bonding in Snowflakes
Dr. S. M. Condren
Dr. S. M. Condren
Hydrogen Bonding in Snowflakes
Dr. S. M. Condren
Dr. S. M. Condren
Logo for ICE
Dr. S. M. Condren
Hydrogen Bonding in H2O
Ice has open lattice-like structure.
Ice density is < liquid and so solid floats on water.
One of the VERY few
substances where
solid is LESS DENSE
than the liquid.
Dr. S. M. Condren
A consequence of
hydrogen bonding
Dr. S. M. Condren
Hydrogen Bonding in H2O
H bonds ---> abnormally high specific heat of water (4.184 J/g•K)
This is the reason water is used to put out fires,
it is the reason
lakes/oceans
control climate,
and is the reason
thunderstorms
release huge
amounts of energy.
Dr. S. M. Condren
Lower
th
9
Ward of New Orleans
10 months after the storm!
Dr. S. M. Condren
Boiling Points of Simple
Hydrogen-Containing Compounds
Dr. S. M. Condren
Methane Hydrate
Dr. S. M. Condren
Hydrogen Bonding in Biology
H-bonding is especially strong in biological systems
— such as DNA.
DNA — helical chains of phosphate groups and
sugar molecules. Chains are helical because of
tetrahedral geometry of P, C, and O.
Chains bind to one another by specific hydrogen
bonding between pairs of Lewis bases.
—adenine with thymine
—guanine with cytosine
Dr. S. M. Condren
Double helix
of DNA
Portion of a
DNA chain
Dr. S. M. Condren
Base-Pairing through H-Bonds
Dr. S. M. Condren
Base-Pairing through H-Bonds
Dr. S. M. Condren
Discovering the Double Helix
Rosalind Franklin,
1920-1958
X-ray photo that led
to structure
James Watson (left) Maurice Wilkins,
1916 - 2004
1928Francis Crick (right)
1916-2004 1962 Nobel Prize for Physiology or Medicine
Dr. S. M. Condren
Forces Involving Induced Dipoles
How can non-polar molecules such as
O2 and I2 dissolve in water?
The water dipole INDUCES a dipole
in the O2 electric cloud.
Dipole-induced
dipole
Dr. S. M. Condren
Forces Involving Induced Dipoles
Solubility increases
with mass of the gas
Process of inducing a dipole is polarization.
Degree to which electron cloud of an atom or molecule can be
distorted is its polarizability.
Dr. S. M. Condren
IM Forces – Induced Dipoles
Consider I2
dissolving
in ethanol,
CH3CH2OH
-
I-I
- O
R
H
+
I-I
The alcohol
temporarily
creates or
INDUCES a
dipole in I2.
Dr. S. M. Condren
+
- O
R
H
+
Forces Involving Induced Dipoles
The magnitude of the induced dipole
depends on the tendency to be distorted.
Higher molecular weight ---> larger
induced dipoles.
Molecule
Boiling Point (oC)
CH4 (methane)
- 161.5
C2H6 (ethane)
- 88.6
C3H8 (propane)
- 42.1
C4H10 (butane)
- 0.5
Dr. S. M. Condren
Boiling Points of Hydrocarbons
C4H10
C3H8
C2H6
CH4
Note linear relation between bp and molar mass.
Dr. S. M. Condren
Intermolecular Forces Summary
Dr. S. M. Condren
Liquids
In a liquid
• molecules are in
constant motion
• there are appreciable
intermolec. forces
• molecules close
together
• Liquids are almost
incompressible
• Liquids do not fill the
container
Dr. S. M. Condren
Liquids
The two key properties we need to
describe are EVAPORATION and its
opposite—CONDENSATION
evaporation--->
LIQUID
Add energy
VAPOR
break IM bonds
make IM bonds
Remove energy
<---condensation
Dr. S. M. Condren
Liquids
Distribution of molecular
energies in a liquid.
KE is proportional to T.
At higher T a much
larger number of
molecules has high
enough energy to
break IM forces and
move from liquid to
vapor state.
High E molecules carry
away E. You cool
down when sweating
or after swimming.
Dr. S. M. Condren
When molecules of liquid are in
the vapor state, they exert a
Liquids
VAPOR PRESSURE
EQUILIBRIUM VAPOR
PRESSURE is the pressure
exerted by a vapor over
a liquid in a closed
container when the
rate of evaporation = rate of condensation.
Dr. S. M. Condren
Measuring Equilibrium
Vapor Pressure
Liquid in flask evaporates and exerts pressure on manometer.
Dr. S. M. Condren
Equilibrium Vapor Pressure
Dr. S. M. Condren
Boiling Point
Liquid boils when its vapor pressure equals
atmospheric pressure.
When pressure is lowered, the vapor pressure
can equal the external pressure at a lower
temperature.
Dr. S. M. Condren
Liquids
If external P = 760 mm Hg, T of boiling is the
NORMAL BOILING POINT
VP of a given molecule at a given T depends
on IM forces. Here the VP’s are in the order
ether
O
C2H5
H5C2
dipoledipole
alcohol
O
H5C2
H
H-bonds
water
O
H
H
extensive
H-bonds
increasing strength of IM interactions
Dr. S. M. Condren
Liquids
HEAT OF VAPORIZATION is the heat
required (at constant P) to vaporize the liquid.
LIQ + heat ---> VAP
Compd.
∆Hvap (kJ/mol) IM Force
H 2O
40.7 (100 oC) H-bonds, dipole,
induced dipole
SO2
26.8 (-47 oC) dipole, induced
dipole
Xe
12.6 (-107 oC) induced dipole
Dr. S. M. Condren
Liquids
Molecules at surface behave differently than those
in the interior.
Molecules at surface experience net INWARD force of
attraction.
This leads to SURFACE TENSION — the energy
required to break the surface.
Dr. S. M. Condren
Liquids
Intermolecular forces also lead to CAPILLARY
action and to the existence of a concave
meniscus for a water column.
concave
meniscus
H2 O in
glass
tube
ADHESIVE FORCES
between water
and glass
COHESIVE FORCES
between water
molecules
Dr. S. M. Condren
Capillary Action
Movement of water up a piece of paper
depends on H-bonds between H2O
and the OH groups of the cellulose in
the paper.
Dr. S. M. Condren
Metallic and Ionic Solids
Dr. S. M. Condren
Types of Solids
TYPE
Ionic
Metallic
Molecular
Network
EXAMPLE
NaCl, CaF2, ZnS
Na, Fe
Ice, I2
Diamond
Graphite
Dr. S. M. Condren
FORCE
Ion-ion
Metallic
Dipole
Ind. dipole
Extended
covalent
Phases Diagrams
—
Important Points
for Water
T(˚C)
Normal boil point
100
Normal freeze point 0
Triple point
0.0098
Critical point
374
Dr. S. M. Condren
P(mmHg)
760
760
4.58
218 atm
Solid-Vapor Equilibria
At P < 4.58 mmHg and T < 0.0098 ˚C
solid H2O can go directly to vapor.
This process is called
SUBLIMATION
This is how a frost-free refrigerator
works.
Dr. S. M. Condren
CO2 Phase Diagram
Dr. S. M. Condren
Network Solids
Diamond
Graphite
Dr. S. M. Condren
Properties of Solids
1. Molecules, atoms or ions
locked into a CRYSTAL
LATTICE
2. Particles are CLOSE
together
3. STRONG IM forces
4. Highly ordered, rigid,
incompressible
ZnS, zinc sulfide
Dr. S. M. Condren
Crystal Lattices
• Regular 3-D arrangements of equivalent
LATTICE POINTS in space.
• Lattice points define UNIT CELLS
– smallest repeating internal unit that has the
symmetry characteristic of the solid.
Dr. S. M. Condren
Cubic Unit Cells
There are 7 basic crystal systems, but we are
only concerned with CUBIC.
All sides
equal length
All angles
are 90 degrees
Dr. S. M. Condren
Cubic Unit Cells of
Metals
Primitive cubic
Dr. S. M. Condren
Simple Cubic Unit Cell
• Each atom is at a corner of a unit cell
and is shared among 8 unit cells.
• Each edge is shared with 4 cells
• Each face is part of two cells.
Dr. S. M. Condren
Atom Sharing
at Cube Faces and Corners
Atom shared in
corner --> 1/8 inside
each unit cell
Atom shared in face
--> 1/2 inside each unit
cell
Dr. S. M. Condren
Number of Atoms per Unit Cell
Unit Cell Type
SC (Primitive Cubic)
BCC
FCC
Net Number Atoms
Primitive cubic
Dr. S. M. Condren
1
2
4
Atom Packing in Unit Cells
Assume atoms are hard spheres and that crystals are built
by PACKING of these spheres as efficiently as possible.
Dr. S. M. Condren
Units Cells for Metals
Primitive cubic
Dr. S. M. Condren
Atom Packing in Unit Cells
Dr. S. M. Condren
Simple Ionic Compounds
Lattices of many simple ionic solids are built
by taking a SC (Simple or Primitive Cubic)
or FCC (Face-Centered Cubic) lattice of
ions of one type and placing ions of
opposite charge in the holes in the lattice.
EXAMPLE: CsCl has a SC (Primitive
Cubic) lattice of Cs+ ions with Cl- in the
center NOT a BCC (Body-Centered Cubic)
because the ion at the center of the body
is not the same ion as at the corners.
Dr. S. M. Condren
Two Views of CsCl Unit Cell
•Lattice can be SC lattice of Cl- with Cs+ in hole
•OR SC lattice of Cs+ with Cl- in hole
•Either arrangement leads to formula of 1 Cs+ and 1 Clper unit cell
Dr. S. M. Condren
NaCl Construction
FCC lattice of Cl- with
Na+ in holes
Na+ in
octahedral
holes
Dr. S. M. Condren
Comparing NaCl and CsCl
• Even though their formulas have one
cation and one anion, the lattices of CsCl
and NaCl are different.
• The different lattices arise from the fact
that a Cs+ ion is much larger than a Na+
ion.
Dr. S. M. Condren
Face-Centered Cubic
Zinc blende
Diamond
Dr. S. M. Condren
Common
Ionic
Solids
Magnesium silicate,
MgSiO3
Dr. S. M. Condren