Polonium-210 Poisoning

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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
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Chapter 13

• Intermolecular Forces Liquids, and Solids

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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?

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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.

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Ion-Ion Forces for comparison of magnitude

• NaCl- in salt
• These are the strongest forces.
• Lead to solids with high melting temperatures.
• NaCl, mp 800 oC
• MgO, mp 2800 oC

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Covalent Bonding Forcesfor comparison of
magnitude
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Attraction Between Ions and Permanent Dipoles

• Water is highly polar and can interact with
  positive and negative ions to give hydrated ions
  in water.

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Attraction Between Ions and Permanent Dipoles

• Many metal ions are hydrated. This is the reason
  metal salts dissolve in water.

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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 --gt M(H2O)xn

-1922 kJ/mol
-405 kJ/mol
-263 kJ/mol
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Dipole-Dipole Forces

• Such forces bind molecules having permanent
  dipoles to one another.

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Dipole-Dipole Forces

• Influence of dipole-dipole forces is seen in the
  boiling points of simple molecules.
• Compd Mol. Wt. Boil Point
• N2 28 -196 oC
• CO 28 -192 oC
• Br2 160 59 oC
• ICl 162 97 oC

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Hydrogen Bonding

• A special form of dipole-dipole attraction, which
  enhances dipole-dipole attractions.

H-bonding is strongest when X and Y are N, O, or F
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H-Bonding Between Methanol and Water
-?
?
-?
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H-Bonding Between Two Methanol Molecules
-?
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H-bond
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H-Bonding Between Ammonia and Water
-?
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H-bond
This H-bond leads to the formation of NH4 and OH-
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Hydrogen Bonding in H2O

• H-bonding is especially strong in water because
• the OH bond is very polar
• there are 2 lone pairs on the O atom
• Accounts for many of waters unique properties.

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Hydrogen Bonding in H2O

• Ice has open lattice-like structure.
• Ice density is lt liquid.
• And so solid floats on water.

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Hydrogen Bonding in Snowflakes
Dr. S. M. Condren
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Hydrogen Bonding in Snowflakes
Dr. S. M. Condren
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Logo for ICE
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Hydrogen Bonding in H2O

• Ice has open lattice-like structure.
• Ice density is lt liquid and so solid floats on
  water.

One of the VERY few substances where solid is
LESS DENSE than the liquid.
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A consequence of hydrogen bonding
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Hydrogen Bonding in H2O

• H bonds ---gt abnormally high specific heat of
  water (4.184 J/gK)
• 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.

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Lower 9th Ward of New Orleans
10 months after the storm!
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Boiling Points of Simple Hydrogen-Containing
Compounds
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Methane Hydrate
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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

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Double helix of DNA
Portion of a DNA chain
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Base-Pairing through H-Bonds
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Base-Pairing through H-Bonds
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Discovering the Double Helix
Rosalind Franklin, 1920-1958 X-ray photo that led
to structure
Maurice Wilkins, 1916 - 2004
James Watson (left) 1928- Francis Crick
(right) 1916-2004
1962 Nobel Prize for Physiology or Medicine
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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
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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.
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IM Forces Induced Dipoles

• Consider I2 dissolving in ethanol, CH3CH2OH

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Forces Involving Induced Dipoles

• The magnitude of the induced dipole depends on
  the tendency to be distorted.
• Higher molecular weight ---gt larger induced
  dipoles.
• Molecule Boiling Point (oC)
• CH4 (methane) - 161.5
• C2H6 (ethane) - 88.6
• C3H8 (propane) - 42.1
• C4H10 (butane) - 0.5

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Boiling Points of Hydrocarbons

• Note linear relation between bp and molar mass.

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Intermolecular Forces Summary
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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

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Liquids

• The two key properties we need to describe are
  EVAPORATION and its oppositeCONDENSATION

evaporation---gt
Add energy
break IM bonds
make IM bonds
Remove energy
lt---condensation
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Liquids

• 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.

Distribution of molecular energies in a liquid.
KE is proportional to T.
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Liquids

• When molecules of liquid are in the vapor state,
  they exert a 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.
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Measuring Equilibrium Vapor Pressure
Liquid in flask evaporates and exerts pressure on
manometer.
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Equilibrium Vapor Pressure
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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.

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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 VPs are in the order

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Liquids

• HEAT OF VAPORIZATION is the heat required (at
  constant P) to vaporize the liquid.
• LIQ heat ---gt VAP
• Compd. ?Hvap (kJ/mol) IM Force
• H2O 40.7 (100 oC) H-bonds, dipole,
  induced dipole
• SO2 26.8 (-47 oC) dipole, induced
  dipole
• Xe 12.6 (-107 oC) induced dipole

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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.
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Liquids

• Intermolecular forces also lead to CAPILLARY
  action and to the existence of a concave meniscus
  for a water column.

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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.

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Metallic and Ionic Solids
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Types of Solids

• TYPE EXAMPLE FORCE
• Ionic NaCl, CaF2, ZnS Ion-ion
• Metallic Na, Fe Metallic
• Molecular Ice,
  I2 Dipole Ind. dipole
• Network Diamond Extended
  Graphite covalent

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Phases Diagrams Important Points for Water

• T(C) P(mmHg)
• Normal boil point 100 760
• Normal freeze point 0 760
• Triple point 0.0098 4.58
• Critical point 374 218 atm

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Solid-Vapor Equilibria

• At P lt 4.58 mmHg and T lt 0.0098 C
• solid H2O can go directly to vapor. This process
  is called SUBLIMATION
• This is how a frost-free refrigerator works.

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CO2 Phase Diagram
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Network Solids
Diamond
Graphite
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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
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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.

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Cubic Unit Cells
There are 7 basic crystal systems, but we are
only concerned with CUBIC.
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Cubic Unit Cells of Metals
Primitive cubic
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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.

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Atom Sharing at Cube Faces and Corners
Atom shared in corner --gt 1/8 inside each unit
cell
Atom shared in face --gt 1/2 inside each unit cell
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Number of Atoms per Unit Cell

• Unit Cell Type Net Number Atoms
• SC (Primitive Cubic)
• BCC
• FCC

1
2
4
Primitive cubic
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Atom Packing in Unit Cells
Assume atoms are hard spheres and that crystals
are built by PACKING of these spheres as
efficiently as possible.
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Units Cells for Metals
Primitive cubic
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Atom Packing in Unit Cells
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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.

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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 Cl- per unit cell

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NaCl Construction
FCC lattice of Cl- with Na in holes
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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.

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Face-Centered Cubic
Zinc blende
Diamond
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Common Ionic Solids

• Magnesium silicate, MgSiO3