1. 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

2. Intermolecular Forces: Liquids, and Solids
Chapter 13
Intermolecular Forces: Liquids, and Solids
Dr. S. M. Condren

3. 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

4. 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

5. Dr. S. M. Condren

6. comparison of magnitude
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

7. 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

8. Attraction Between Ions and Permanent Dipoles
Water is highly polar and can interact with positive and negative ions to give hydrated ions in water.
Dr. S. M. Condren

9. Attraction Between Ions and Permanent Dipoles
Many metal ions are hydrated. This is the reason metal salts dissolve in water.
Dr. S. M. Condren

10. Mn+ + xH2O --> [M(H2O)x]n+
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+
-1922 kJ/mol
-405 kJ/mol
-263 kJ/mol
Dr. S. M. Condren

11. Dipole-Dipole Forces
Such forces bind molecules having permanent dipoles to one another.
Dr. S. M. Condren

12. Dipole-Dipole Forces
Influence of dipole-dipole forces is seen in the boiling points of simple molecules.
Comp’d Mol. Wt. Boil Point
N oC
CO oC
Br oC
ICl oC
Dr. S. M. Condren

13. 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
Dr. S. M. Condren

14. H-Bonding Between
Methanol and Water -
H-bond + -
Dr. S. M. Condren

15. Two Methanol Molecules
H-Bonding Between
Two Methanol Molecules - + -
H-bond
Dr. S. M. Condren

16. H-Bonding Between Ammonia and Water H-bond - + -
This H-bond leads to the formation of NH4+ and OH-
Dr. S. M. Condren

17. 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

18. Hydrogen Bonding in H2O Ice has open lattice-like structure.
Ice density is < liquid.
And so solid floats on water.
Dr. S. M. Condren

19. Hydrogen Bonding in Snowflakes
Dr. S. M. Condren
Dr. S. M. Condren

20. Hydrogen Bonding in Snowflakes
Dr. S. M. Condren
Dr. S. M. Condren

21. Logo for ICE
Dr. S. M. Condren

22. 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

23. A consequence of hydrogen bonding
Dr. S. M. Condren

24. 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

25. Lower 9th Ward of New Orleans
Dr. S. M. Condren
10 months after the storm!

26. Boiling Points of Simple Hydrogen-Containing Compounds
Dr. S. M. Condren

27. Methane Hydrate
Dr. S. M. Condren

28. 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

29. Double helix of DNA Portion of a DNA chain
Dr. S. M. Condren

30. Base-Pairing through H-Bonds
Dr. S. M. Condren

31. Base-Pairing through H-Bonds
Dr. S. M. Condren

32. Discovering the Double Helix
Rosalind Franklin,
X-ray photo that led to structure
Maurice Wilkins,
James Watson (left)
1928-
Francis Crick (right)
1962 Nobel Prize for Physiology or Medicine
Dr. S. M. Condren

33. Dipole-induced dipole
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

34. 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

35. The alcohol temporarily creates or INDUCES a dipole in I2.
IM Forces – Induced Dipoles
Consider I2 dissolving in ethanol, CH3CH2OH O H - d +
I-I R
The alcohol temporarily creates or INDUCES a dipole in I2.
Dr. S. M. Condren

36. 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)
C2H6 (ethane)
C3H8 (propane)
C4H10 (butane)
Dr. S. M. Condren

37. Boiling Points of Hydrocarbons
CH4
C2H6
C3H8
C4H10
Note linear relation between bp and molar mass.
Dr. S. M. Condren

38. Intermolecular Forces Summary
Dr. S. M. Condren

39. 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
Liquids
Dr. S. M. Condren

40. 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

41. 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.
Liquids
Distribution of molecular energies in a liquid.
KE is proportional to T.
Dr. S. M. Condren

42. Liquids EQUILIBRIUM VAPOR PRESSURE is the pressure
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.
Dr. S. M. Condren

43. Measuring Equilibrium Vapor Pressure
Liquid in flask evaporates and exerts pressure on manometer.
Dr. S. M. Condren

44. Equilibrium Vapor Pressure
Dr. S. M. Condren

45. 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

46. 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 C 2 H 5
water
alcohol
ether
increasing strength of IM interactions
extensive
H-bonds
dipole-
dipole O
Dr. S. M. Condren

47. Liquids
HEAT OF VAPORIZATION is the heat required (at constant P) to vaporize the liquid.
LIQ heat ---> VAP
Compd. ∆Hvap (kJ/mol) IM Force
H2O (100 oC) H-bonds, dipole, induced dipole
SO (-47 oC) dipole, induced dipole
Xe (-107 oC) induced dipole
Dr. S. M. Condren

48. 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

49. Liquids
Intermolecular forces also lead to CAPILLARY action and to the existence of a concave meniscus for a water column.
concave
meniscus
ADHESIVE FORCES
between water
and glass H 2
O in
glass
tube
COHESIVE FORCES
between water
molecules
Dr. S. M. Condren

50. 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

51. Metallic and Ionic Solids
Dr. S. M. Condren

52. 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
Dr. S. M. Condren

53. Phases Diagrams — Important Points for Water
T(˚C) P(mmHg)
Normal boil point
Normal freeze point
Triple point
Critical point atm
Dr. S. M. Condren

54. Solid-Vapor Equilibria
At P < 4.58 mmHg and T < ˚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

55. CO2 Phase Diagram
Dr. S. M. Condren

56. Network Solids
Diamond
Graphite
Dr. S. M. Condren

57. 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

58. 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

59. 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

60. Cubic Unit Cells of Metals
Primitive cubic
Dr. S. M. Condren

61. 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

62. 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

63. Number of Atoms per Unit Cell
Unit Cell Type Net Number Atoms
SC (Primitive Cubic)
BCC
FCC 1 2 4
Primitive cubic
Dr. S. M. Condren

64. 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

65. Units Cells for Metals
Primitive cubic
Dr. S. M. Condren

66. Atom Packing in Unit Cells
Dr. S. M. Condren

67. 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

68. 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
Dr. S. M. Condren

69. NaCl Construction Na+ in octahedral holes
FCC lattice of Cl- with Na+ in holes
Dr. S. M. Condren

70. 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

71. Face-Centered Cubic
Diamond
Zinc blende
Dr. S. M. Condren

72. Common Ionic Solids
Magnesium silicate, MgSiO3
Dr. S. M. Condren