Dr. S. M. Condren Polonium-210 Poisoning #atoms Po 210 = (1.0 gPo 210 Cl 2 )(1g/10 6 g) (6.02x10 23...
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Transcript of Dr. S. M. Condren Polonium-210 Poisoning #atoms Po 210 = (1.0 gPo 210 Cl 2 )(1g/10 6 g) (6.02x10 23...
Dr. S. M. Condren
Polonium-210 Poisoning#atoms Po210 = (1.0gPo210Cl2) (1g/106g)
(6.02x1023atoms/mol) (1mol/280gPoCl2)
= 2.2x1015 atomst1/2 = 138 days by decay of 5.3MeV energy
10a few hundred atoms Po-110 per cellEven if only 10% decay, 110 decays per cell
Chemical & Engineering News, Dec. 4, 2006 pg.15
Former Russian spy died 22 days after the poisoning incident.The Po210 would decay by a little more than 10% in 22 days.
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
Now turn to forces between molecules
— INTERmolecular forces.
Forces between molecules/atoms, between ions, or between molecules/atoms and ions.
Inter-molecular ForcesHave studied INTRAmolecular forces— the forces holding atoms together to form molecules.
Dr. S. M. Condren
Dr. S. M. Condren
NaNa++—Cl—Cl-- in salt in salt
These are the strongest forces.
Lead to solids with Lead to solids with high melting high melting temperatures.temperatures.
NaCl, mp = 800 oC
MgO, mp = 2800 MgO, mp = 2800 ooCC
Ion-Ion Forces for comparison of magnitude
Dr. S. M. Condren
C–H, 413 kJ/molC–H, 413 kJ/mol
C=C, 610 kJ/molC=C, 610 kJ/mol
C–C, 346 kJ/molC–C, 346 kJ/mol
CN, 887 kJ/molCN, 887 kJ/mol
Covalent Bonding Forcesfor comparison of magnitude
Dr. S. M. Condren
Water is highly polar and Water is highly polar and can interact with positive can interact with positive and negative ions to give and negative ions to give
hydrated ions in water.ions in water.
HH
water dipole
••
••
O-
+
Attraction Between Ionsand Permanent Dipoles
Dr. S. M. Condren
Many metal ions are hydrated. Many metal ions are hydrated. This is the reason metal salts This is the reason metal salts dissolve in waterdissolve in water..
Attraction Between Ionsand Permanent Dipoles
Dr. S. M. Condren
Attraction between ions and dipole depends Attraction between ions and dipole depends on on ion charge and and ion-dipole distance..
Measured by ∆H for Measured by ∆H for
MMn+n+ + xH + xH22O O --> [M(H [M(H22O)O)xx]]n+n+
-1922 kJ/mol-1922 kJ/mol -405 kJ/mol-405 kJ/mol -263 kJ/mol-263 kJ/mol
OH
H+
-• • • O
H
H+
-• • • O
H
H+
-• • •
Na+Mg2+
Cs+
Attraction Between Ionsand Permanent Dipoles
Dr. S. M. Condren
Such forces bind molecules Such forces bind molecules having permanent dipoles to one having permanent dipoles to one another.another.
Dipole-Dipole Forces
Dr. S. M. Condren
Influence of dipole-dipole forces is seen Influence of dipole-dipole forces is seen in the boiling points of simple in the boiling points of simple molecules.molecules.
Comp’dComp’d Mol. Wt.Mol. Wt. Boil PointBoil Point
NN22 2828 -196 -196 ooCC
COCO 2828 -192 -192 ooCC
BrBr22 160160 59 59 ooCC
IClICl 162162 97 97 ooCC
Dipole-Dipole Forces
Dr. S. M. Condren
A special form of dipole-dipole A special form of dipole-dipole attraction, which enhances dipole-attraction, which enhances dipole-dipole attractions.dipole attractions.
Hydrogen Bonding
H-bonding is strongest when X and Y are N, O, or F
Dr. S. M. Condren
H-bondH-bondH-bondH-bond--
++
--
H-Bonding BetweenMethanol and Water
Dr. S. M. Condren
H-bondH-bondH-bondH-bond
--++
--
H-Bonding BetweenTwo Methanol Molecules
Dr. S. M. Condren
--
++ --
This H-bond leads to the formation of This H-bond leads to the formation of NHNH44
++ and OH and OH--
H-Bonding BetweenAmmonia and Water
H-bond
Dr. S. M. Condren
H-bonding is H-bonding is especially strong in especially strong in water becausewater because
• the O—H bond is the O—H bond is very polarvery polar
• there are 2 lone there are 2 lone pairs on the O atompairs on the O atom
Accounts for many of Accounts for many of water’s unique water’s unique properties.properties.
Hydrogen Bonding in H2O
Dr. S. M. Condren
Ice has open Ice has open lattice-like lattice-like structure.structure.
Ice density is Ice density is < liquid.< liquid.
And so solid And so solid floats on floats on water.water.
Hydrogen Bonding in H2O
Dr. S. M. CondrenDr. S. M. Condren
Hydrogen Bonding in Snowflakes
Dr. S. M. CondrenDr. S. M. Condren
Hydrogen Bonding in Snowflakes
Dr. S. M. Condren
Logo for ICE
Dr. S. M. Condren
Ice has open lattice-like structure.Ice has open lattice-like structure.
Ice density is < liquid and so solid floats on water.Ice density is < liquid and so solid floats on water.
One of the VERY few One of the VERY few substances where substances where solid is LESS DENSE solid is LESS DENSE than the liquid.than the liquid.
Hydrogen Bonding in H2O
Dr. S. M. Condren
A consequence ofhydrogen bonding
Dr. S. M. Condren
H bonds ---> abnormally high specific heat of water (4.184 J/g•K)H bonds ---> abnormally high specific heat of water (4.184 J/g•K)
This is the reason water is used to put out fires,This is the reason water is used to put out fires,
it is the reason it is the reason lakes/oceans lakes/oceans control climate,control climate,
and is the reason and is the reason thunderstorms thunderstorms release huge release huge amounts of energy.amounts of energy.
Hydrogen Bonding in H2O
Dr. S. M. Condren
Lower 9th 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
H-bonding is especially strong in biological systems H-bonding is especially strong in biological systems — such as DNA. — such as DNA.
DNA — helical chains of phosphate groups and DNA — helical chains of phosphate groups and sugar molecules. Chains are helical because of sugar molecules. Chains are helical because of tetrahedral geometry of P, C, and O.tetrahedral geometry of P, C, and O.
Chains bind to one another by specific hydrogen Chains bind to one another by specific hydrogen bonding between pairs of Lewis bases.bonding between pairs of Lewis bases.
——adenine with thymineadenine with thymine
——guanine with cytosineguanine with cytosine
Hydrogen Bonding in Biology
Dr. S. M. Condren
Portion of a Portion of a DNA chainDNA chain
Double helix Double helix of DNAof DNA
Dr. S. M. Condren
Base-Pairing through H-Bonds
Dr. S. M. Condren
Base-Pairing through H-Bonds
Dr. S. M. Condren
James Watson (left)James Watson (left)1928-1928-Francis Crick (right)Francis Crick (right)1916-20041916-2004
Rosalind Franklin, Rosalind Franklin, 1920-19581920-1958X-ray photo that led X-ray photo that led to structureto structure
Maurice Wilkins, Maurice Wilkins, 1916 - 20041916 - 2004
1962 Nobel Prize for Physiology or Medicine
Discovering the Double Helix
Dr. S. M. Condren
How can non-polar molecules such as How can non-polar molecules such as OO2 2 and Iand I22 dissolve in water? dissolve in water?The water dipole The water dipole INDUCES a dipole a dipole in the Oin the O22 electric cloud. electric cloud.
Dipole-induced Dipole-induced dipoledipole
Dipole-induced Dipole-induced dipoledipole
Forces Involving Induced Dipoles
Dr. S. M. Condren
Solubility increases Solubility increases with mass of the gaswith 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 Degree to which electron cloud of an atom or molecule can be distorted is its distorted is its polarizability..
Dr. S. M. Condren
Consider IConsider I22
dissolving dissolving in ethanol, in ethanol, CHCH33CHCH22OHOH
OH
-
+
I-I
R-
+
OH
+
-
I-I
R
The alcohol The alcohol temporarily temporarily creates or creates or INDUCESINDUCES a a dipole in Idipole in I22..
IM Forces – Induced Dipoles
Dr. S. M. Condren
The magnitude of the induced dipole The magnitude of the induced dipole depends on the tendency to be distorted. depends on the tendency to be distorted.
Higher molecular weight ---> larger Higher molecular weight ---> larger induced dipoles.induced dipoles.
MoleculeMolecule Boiling Point Boiling Point ((ooC)C)
CHCH44 (methane) (methane) - 161.5- 161.5
CC22HH66 (ethane) (ethane) - 88.6 - 88.6
CC33HH88 (propane) (propane) - 42.1- 42.1
CC44HH1010 (butane) (butane) - 0.5- 0.5
Forces Involving Induced Dipoles
Dr. S. M. Condren
Boiling Points of Hydrocarbons
Note linear relation between bp and molar mass.
CHCH44
CC22HH66
CC33HH88
CC44HH1010
Dr. S. M. Condren
Intermolecular Forces Summary
Dr. S. M. Condren
In a liquidIn a liquid•• molecules are in molecules are in
constant motionconstant motion
•• there are appreciable there are appreciable intermolec. forcesintermolec. forces
•• molecules close molecules close togethertogether
•• Liquids are almost Liquids are almost incompressibleincompressible
•• Liquids do not fill the Liquids do not fill the containercontainer
Liquids
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 The two key properties we need to describe are describe are EVAPORATION and its and its opposite—opposite—CONDENSATION
Dr. S. M. Condren
Liquids At higher T a much At higher T a much larger number of larger number of molecules has high molecules has high enough energy to enough energy to break IM forces and break IM forces and move from liquid to move from liquid to vapor state.vapor state.
High E molecules carry High E molecules carry away E. You cool away E. You cool down when sweating down when sweating or after swimming.or after swimming.
.
0
Num
ber
of m
olec
ules
Molecular energy
minimum energy neededto break IM forces and evaporate
higher Tlower T
Distribution of molecular energies in a liquid. KE is proportional to T.
Dr. S. M. Condren
LiquidsWhen molecules of liquid are in When molecules of liquid are in the vapor state, they exert a the vapor state, they exert a VAPOR PRESSURE
EQUILIBRIUM VAPOR PRESSURE is the pressure is the pressure exerted by a vapor over exerted by a vapor over a liquid in a closed a liquid in a closed container when the 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
When pressure is lowered, the vapor pressure When pressure is lowered, the vapor pressure can equal the external pressure at a lower can equal the external pressure at a lower temperature.temperature.
Liquid boils when its vapor pressure equals atmospheric pressure.
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 VP of a given molecule at a given T depends
on IM forces. Here the VP’s are in the orderon IM forces. Here the VP’s are in the order
Liquids
C2H5H5C2 HH5C2 HH
wateralcoholether
increasing strength of IM interactions
extensiveH-bondsH-bonds
dipole-dipole
OOO
Dr. S. M. Condren
LiquidsHEAT OF VAPORIZATION is the heat is the heat
required (at constant P) to vaporize the liquid.required (at constant P) to vaporize the liquid.LIQ + heat ---> VAPLIQ + heat ---> VAP
Compd.Compd. ∆H∆Hvapvap (kJ/mol) (kJ/mol) IM ForceIM Force
HH22OO 40.7 (100 40.7 (100 ooC)C) H-bonds, dipole, H-bonds, dipole, induced dipoleinduced dipole
SOSO22 26.8 (-47 26.8 (-47 ooC)C) dipole, induced dipole, induced dipole dipole
XeXe 12.6 (-107 12.6 (-107 ooC)C) induced dipole induced dipole
Dr. S. M. Condren
LiquidsMolecules at surface behave differently than those Molecules at surface behave differently than those
in the interior.in the interior.
Molecules at surface experience net INWARD force of Molecules at surface experience net INWARD force of attraction. attraction. This leads to This leads to SURFACE TENSION — the energy — the energy required to break the surface.required to break the surface.
Dr. S. M. Condren
LiquidsIntermolecular forces also lead to Intermolecular forces also lead to CAPILLARY
action and to the existence of a concave action and to the existence of a concave meniscus for a water column.meniscus for a water column.
concavemeniscus
H2O in
glasstube
ADHESIVE FORCESbetween waterand glass
COHESIVE FORCESbetween watermolecules
Dr. S. M. Condren
Capillary Action
Movement of water up a piece of paper Movement of water up a piece of paper depends on H-bonds between Hdepends on H-bonds between H22O O
and the OH groups of the cellulose in and the OH groups of the cellulose in the paper.the paper.
Dr. S. M. Condren
Metallic and Ionic Solids
Dr. S. M. Condren
Types of SolidsTYPE EXAMPLE FORCE
Ionic Ionic NaCl, CaF NaCl, CaF22, ZnS, ZnS Ion-ionIon-ion
MetallicMetallic Na, Fe Na, Fe MetallicMetallic
MolecularMolecular Ice, I Ice, I22 DipoleDipole
Ind. dipole Ind. dipole
NetworkNetwork Diamond Diamond ExtendedExtended Graphite Graphite covalent covalent
Dr. S. M. Condren
Phases Diagrams —Important Points for
WaterT(˚C) P(mmHg)
Normal boil point 100 760
Normal freeze point 0 760
Triple point 0.0098 4.58
Critical point 374374 218 218 atm atm
Dr. S. M. Condren
Solid-Vapor Equilibria
At P < 4.58 mmHg and T < 0.0098 ˚CAt P < 4.58 mmHg and T < 0.0098 ˚C
solid Hsolid H22O can go directly to vapor. O can go directly to vapor.
This process is called This process is called SUBLIMATION
This is how a frost-free refrigerator This is how a frost-free refrigerator works.works.
Dr. S. M. Condren
CO2 Phase Diagram
Dr. S. M. Condren
Network Solids
DiamondDiamond
GraphiteGraphite
Dr. S. M. Condren
Properties of Solids
1.1. Molecules, atoms or ions Molecules, atoms or ions
locked into a locked into a CRYSTAL LATTICE
2. Particles are CLOSE 2. Particles are CLOSE togethertogether
3. STRONG IM forces3. STRONG IM forces
4. Highly ordered, rigid, 4. Highly ordered, rigid, incompressibleincompressible
ZnS, zinc sulfideZnS, zinc sulfide
Dr. S. M. Condren
Crystal Lattices• Regular 3-D arrangements of equivalent Regular 3-D arrangements of equivalent
LATTICE POINTS in space.LATTICE POINTS in space.• Lattice points define Lattice points define UNIT CELLS
– smallest repeating internal unit that has the smallest repeating internal unit that has the
symmetry characteristic of the solid.symmetry characteristic of the solid.
Dr. S. M. Condren
Cubic Unit Cells
All anglesare 90 degrees
All sidesequal length
There are 7 basic crystal systems, but we are There are 7 basic crystal systems, but we are
only concerned withonly concerned with CUBIC..
Dr. S. M. Condren
Cubic Unit Cells of Metals
Primitive cubic
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
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 Unit Cell Type Net Number AtomsNet Number AtomsSC (Primitive Cubic)SC (Primitive Cubic)
BCCBCC FCCFCC
112244
Primitive cubic
Dr. S. M. Condren
Atom Packing in Unit Cells
Assume atoms are hard spheres and that crystals are built Assume atoms are hard spheres and that crystals are built by by PACKING of these spheres as efficiently as possible. 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 Lattices of many simple ionic solids are built by taking a SC (Simple or Primitive Cubic) by taking a SC (Simple or Primitive Cubic) or FCC (Face-Centered Cubic) lattice of or FCC (Face-Centered Cubic) lattice of ions of one type and placing ions of ions of one type and placing ions of opposite charge in the holes in the lattice.opposite charge in the holes in the lattice.
EXAMPLE: CsCl has a SC (Primitive CsCl has a SC (Primitive Cubic) lattice of CsCubic) lattice of Cs++ ions with Cl ions with Cl-- in the in the center NOT a BCC (Body-Centered Cubic) center NOT a BCC (Body-Centered Cubic) because the ion at the center of the body because the ion at the center of the body is not the same ion as at the corners.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 Cl- per unit cell
Dr. S. M. Condren
NaCl Construction
FCC lattice of Cl- with Na+ in holes
NaNa++ in in octahedral octahedral holesholes
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 CubicDiamond Zinc blende
Dr. S. M. Condren
Common Ionic Solids
Magnesium silicate, MgSiO3