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Dr. S. M. Condren Polonium-210 Poisoning #atoms Po 210 = (1.0 gPo 210 Cl 2 )(1g/10 6 g) (6.02x10 23 atoms/mol) (1mol/280gPoCl 2 ) = 2.2x10 15 atoms t 1/2.

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Presentation on theme: "Dr. S. M. Condren Polonium-210 Poisoning #atoms Po 210 = (1.0 gPo 210 Cl 2 )(1g/10 6 g) (6.02x10 23 atoms/mol) (1mol/280gPoCl 2 ) = 2.2x10 15 atoms t 1/2."— Presentation transcript:

1 Dr. S. M. Condren Polonium-210 Poisoning #atoms Po 210 = (1.0 gPo 210 Cl 2 )(1g/10 6 g) (6.02x10 23 atoms/mol) (1mol/280gPoCl 2 ) = 2.2x10 15 atoms t 1/2 = 138 days by decay of 5.3MeV energy 10 a few hundred atoms Po-110 per cell Even if only 10% decay, 1 10 decays per cell Chemical & Engineering News, Dec. 4, 2006 pg.15 Former Russian spy died 22 days after the poisoning incident. The Po 210 would decay by a little more than 10% in 22 days.

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

3 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 I 2 a solid whereas Cl 2 is a gas? Why are NaCl crystals little cubes?

4 Dr. S. M. Condren Now turn to forces between molecules INTER molecular forces. Forces between molecules/atoms, between ions, or between molecules/atoms and ions. Inter-molecular Forces Have studied INTRAmolecular forces the forces holding atoms together to form molecules.

5 Dr. S. M. Condren

6 Na + Cl - in salt These are the strongest forces. Lead to solids with high melting temperatures. NaCl, mp = 800 o C MgO, mp = 2800 o C Ion-Ion Forces for comparison of magnitude

7 Dr. S. M. Condren C–H, 413 kJ/mol C=C, 610 kJ/mol C–C, 346 kJ/mol CN, 887 kJ/mol Covalent Bonding Forces for comparison of magnitude

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

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

10 Dr. S. M. Condren Attraction between ions and dipole depends on and. Attraction between ions and dipole depends on ion charge and ion-dipole distance. Measured by H for M n+ + xH 2 O [M(H 2 O) x ] n+ M n+ + xH 2 O --> [M(H 2 O) x ] n kJ/mol -405 kJ/mol -263 kJ/mol Attraction Between Ions and Permanent Dipoles

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

12 Dr. S. M. Condren Influence of dipole-dipole forces is seen in the boiling points of simple molecules. CompdMol. Wt.Boil Point N o C CO o C Br o C ICl16297 o C Dipole-Dipole Forces

13 Dr. S. M. Condren A special form of dipole-dipole attraction, which enhances dipole- dipole attractions. Hydrogen Bonding H-bonding is strongest when X and Y are N, O, or F

14 Dr. S. M. CondrenH-bondH-bond H-Bonding Between Methanol and Water

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

16 Dr. S. M. Condren This H-bond leads to the formation of NH 4 + and OH - H-Bonding Between Ammonia and Water H-bond

17 Dr. S. M. Condren H-bonding is especially strong in water because the OH bond is very polarthe OH bond is very polar there are 2 lone pairs on the O atomthere are 2 lone pairs on the O atom Accounts for many of waters unique properties. Hydrogen Bonding in H 2 O

18 Dr. S. M. Condren Ice has open lattice-like structure. Ice density is < liquid. And so solid floats on water. Hydrogen Bonding in H 2 O

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

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

21 Dr. S. M. Condren Logo for ICE

22 Dr. S. M. Condren 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. Hydrogen Bonding in H 2 O

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

24 Dr. S. M. Condren H bonds ---> 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, it is the reason lakes/oceans control climate, and is the reason thunderstorms release huge amounts of energy. and is the reason thunderstorms release huge amounts of energy. Hydrogen Bonding in H 2 O

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

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

27 Dr. S. M. Condren Methane Hydrate

28 Dr. S. M. Condren 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 adenine with thymine guanine with cytosine guanine with cytosine Hydrogen Bonding in Biology

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

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

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

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

33 Dr. S. M. Condren How can non-polar molecules such as O 2 and I 2 dissolve in water? The water dipole a dipole in the O 2 electric cloud. The water dipole INDUCES a dipole in the O 2 electric cloud. Dipole-induced dipole Forces Involving Induced Dipoles

34 Dr. S. M. Condren Solubility increases with mass of the gas Forces Involving Induced Dipoles Process of inducing a dipole is. Process of inducing a dipole is polarization. Degree to which electron cloud of an atom or molecule can be distorted is its. Degree to which electron cloud of an atom or molecule can be distorted is its polarizability.

35 Dr. S. M. Condren Consider I 2 dissolving in ethanol, CH 3 CH 2 OH O H - + I-I R - + O H + - I-I R The alcohol temporarily creates or INDUCES a dipole in I 2. IM Forces – Induced Dipoles

36 Dr. S. M. Condren The magnitude of the induced dipole depends on the tendency to be distorted. Higher molecular weight ---> larger induced dipoles. MoleculeBoiling Point ( o C) MoleculeBoiling Point ( o C) CH 4 (methane) CH 4 (methane) C 2 H 6 (ethane) C 2 H 6 (ethane) C 3 H 8 (propane) C 3 H 8 (propane) C 4 H 10 (butane) C 4 H 10 (butane) Forces Involving Induced Dipoles

37 Dr. S. M. Condren Boiling Points of Hydrocarbons Note linear relation between bp and molar mass. CH 4 C2H6C2H6C2H6C2H6 C3H8C3H8C3H8C3H8 C 4 H 10

38 Dr. S. M. Condren Intermolecular Forces Summary

39 Dr. S. M. Condren In a liquid molecules are in constant motionmolecules are in constant motion there are appreciable intermolec. forcesthere are appreciable intermolec. forces molecules close togethermolecules close together Liquids are almost incompressibleLiquids are almost incompressible Liquids do not fill the containerLiquids do not fill the container Liquids

40 Dr. S. M. Condren Liquids break IM bonds make IM bonds Add energy Remove energy LIQUID VAPOR <---condensation evaporation---> The two key properties we need to describe are and its opposite The two key properties we need to describe are EVAPORATION and its oppositeCONDENSATION

41 Dr. S. M. Condren 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.

42 Dr. S. M. Condren Liquids When molecules of liquid are in the vapor state, they exert a When molecules of liquid are in the vapor state, they exert a VAPOR PRESSURE EQUILIBRIUM VAPOR is the pressure PRESSURE is the pressure exerted by a vapor over a liquid in a closed container when the rate of evaporation = rate of condensation.

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

44 Dr. S. M. Condren Equilibrium Vapor Pressure

45 Dr. S. M. Condren Boiling Point When pressure is lowered, the vapor pressure can equal the external pressure at a lower temperature. Liquid boils when its vapor pressure equals atmospheric pressure.

46 Dr. S. M. Condren If external P = 760 mm Hg, T of boiling is the 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 Liquids C 2 H 5 H 5 C 2 H H 5 C 2 H H wateralcoholether increasing strength of IM interactions extensive H-bonds dipole- dipole O O O

47 Dr. S. M. Condren Liquids is the heat required (at constant P) to vaporize the liquid. HEAT OF VAPORIZATION is the heat required (at constant P) to vaporize the liquid. LIQ + heat ---> VAP Compd.H vap (kJ/mol) IM Force H 2 O40.7 (100 o C)H-bonds, dipole, induced dipole SO (-47 o C)dipole, induced dipole Xe12.6 (-107 o C)induced dipole

48 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 the energy required to break the surface. This leads to SURFACE TENSION the energy required to break the surface.

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

50 Dr. S. M. Condren Capillary Action Movement of water up a piece of paper depends on H-bonds between H 2 O and the OH groups of the cellulose in the paper.

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

52 Dr. S. M. Condren Types of Solids TYPEEXAMPLEFORCE Ionic NaCl, CaF 2, ZnSIon-ion Metallic Na, FeMetallic Molecular Ice, I 2 Dipole Ind. dipole Network Diamond Extended Graphite covalent

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

54 Dr. S. M. Condren Solid-Vapor Equilibria At P < 4.58 mmHg and T < ˚C solid H 2 O can go directly to vapor. This process is called solid H 2 O can go directly to vapor. This process is called SUBLIMATION This is how a frost-free refrigerator works.

55 Dr. S. M. Condren CO 2 Phase Diagram

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

57 Dr. S. M. Condren Properties of Solids 1. Molecules, atoms or ions locked into a 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

58 Dr. S. M. Condren Crystal Lattices Regular 3-D arrangements of equivalent LATTICE POINTS in space.Regular 3-D arrangements of equivalent LATTICE POINTS in space. Lattice points defineLattice points define UNIT CELLS –smallest repeating internal unit that has the symmetry characteristic of the solid.

59 Dr. S. M. Condren Cubic Unit Cells All angles are 90 degrees All sides equal length There are 7 basic crystal systems, but we are only concerned with. There are 7 basic crystal systems, but we are only concerned with CUBIC.

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

61 Dr. S. M. Condren 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. Simple Cubic Unit Cell

62 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

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

64 Dr. S. M. Condren Atom Packing in Unit Cells Assume atoms are hard spheres and that crystals are built by of these spheres as efficiently as possible. Assume atoms are hard spheres and that crystals are built by PACKING of these spheres as efficiently as possible.

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

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

67 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. 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. 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.

68 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 Cl - per unit cell

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

70 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.

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

72 Dr. S. M. Condren Common Ionic Solids Magnesium silicate, MgSiO 3


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