Q. Are we ready for complex covalent molecules yet? A. Almost.

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Q. Are we ready for complex covalent molecules
yet?A. Almost.
Astaxanthin, a member of the carotenoid family,
is part of a nutritious dietfor lobsters and
shrimp. These crustaceans bind astaxanthin to the
protein ß-crustacyanin, which changes the shape
of the astaxanthin molecules, turning them a
gray-blue color. Cooking releases the molecules,
returning them to their original bright red
color.
cook
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So far, covalent bonding has been described as
totally equal sharing. Sometimes, sharing is
60-40 or 70-30.
H

Cl kinda hogs the electron. H gets 2 (not
8 because H cant handle 8)
H
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Many bonds are polarized.
Electrons preferentially circulate around the
chlorine atom, taking up more space there.
d
H
d-
Cl
What about the sex life of bowling pins?
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• Magnetic Fleas

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Covalent molecules with more than 2 atoms are
slightly more complex.Example CO2
Bonds polar Molecule not polar.
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The shape of a molecule is determined by
electron-electron repulsion.
O
C
O
The first bond (gray) is normal the second one
(orange its one bond in two parts) lies above
below the first bondthink of p -type orbitals.
All there is to VSEPR theory How can electrons
be as far apart as possible?
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Bungee Time Are those C-O bonds polar?
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If there are more than 2 atoms in the molecule,
the existence of polarized bonds does not
necessarily make the whole molecule
polarized.It depends on symmetry.
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The individual C-O bonds are polar, but the
effect cancels due to symmetry when we consider
the whole CO2 molecule. The CO2 molecule is not
polar. Despite pretty high mass (44x
hydrogen) it is still a gas at normal
temperatures.
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If there are more than 2 atoms in the molecule,
the existence of polarized bonds does not
necessarily make the whole molecule polarized.
F
1. Are the bonds polar? 2. Is the molecule polar?
Always 2 questions
B
This is configuration of atoms is called trigonal
planar.
BF3 is a toxic gas, useful for synthesizing
various chemicals.
This molecule violates the octet rule. Oh, well.
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Lets try methane, CH4
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How can we spread out 4 hydrogens and their
electrons?
H
90o
C
H
H
?
H
Right idea, but we forgot an important detail.
Nothing constrains the 4 electron clouds to exist
in 2D!
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Lets illustrate this with models.
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Tetrahedron to draw this thing, we learn to draw
a cube first. Then locate the lower and upper
crossed vertices. This shape is important!
C
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Water is the most amazing covalent molecule.
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What is the shape of water?
H
O
H
Right idea, but we forgot an important detail.
Nothing constrains those electron clouds to exist
in 2D!
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Tetrahedron to draw this thing, we learn to draw
a cube first. Then locate the lower and upper
crossed vertices. This shape is important!
O
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So water isnt straight!
Electrons comin at ya!
Electrons Going away from you!
O
Electrons in the plane of the blackboard ummscr
een.
H
H
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Its great not to be straight!
Despite its low mass (18 x hydrogen) water is a
liquid at normal temperatures. Dipole-dipole
forces! Explains high boiling high heat
capacity, surface tension.
This is not a social commentary.
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http//www.graphicmaps.com/webimage/ countrys/name
rica/usstates/artwork/rivers/ uslayout.htm ?
? Missouri-Yellowstone confluence
http//www.airphotona.com/image.asp? imageid810c
atnum11200
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Lets do a thought experiment(gedanken
experiment). What happens if three people aim
water cannons at a ball? Can the ball be
suspended in mid-air?
See also http//www.youtube.com/watch?vRqrdcVCZ7
94
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This is a good time to introduce Concept Maps

• http//classes.aces.uiuc.edu/ACES100/Mind/CMap.htm
  l
• http//classes.aces.uiuc.edu/ACES100/Mind/CMap.htm
  l

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This concept map addresses the following
question Are molecules polar?
Electronegative elements (Northeast elements)
Suck Electrons
Atoms identical
Atoms NOT identical
Bond Not Polar
Bond Polar
Symmetrical? Yes No
Molecule polar
Molecule not polar
Example H2
Example CH4
Example CFH3
Why all 4 H atoms pull electrons equally and
Symmetrically from C so forces balance
Why the 3 H atoms pull electrons down, but not
as hard as the F atom pulls up.
Result CFH3 has higher melting point (-142)
than CH4 (-182) than H2 (-253).
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Happy St. Patricks Day (Late) Green l 530 nm
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More complex molecules
OOPS!
OOPS!
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Sudan I dye a.k.a. Solvent Orange R
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Some covalent structures make ions after that,
treat them as ions.
So far, we have seen only atomic ions Na2O,
NaCl, CaCl2 There are also "molecular ions" -
covalent molecules can have a charge ! e.g.
Sulfate ion SO42- How many valence electrons ?
S 6 x 1 6 O 6 x 4 24 Charge 2- 2
32 e- total
If it looks like a duck, swims like a duck, and
quacks like a duck, then it probably is a duck.
Molecular ions pass the duck test.
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What does this molecular ion look like?
You need to be told that the sulfur is in
center. (When in doubt, assume the least
prevalent atom is centered.) put electrons in
to bond O to S (takes 8) satisfy octet for
oxygen (takes 24) total used 32 electrons OK
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Treat the molecular ion similar to an atomic one.
Sulfate has 2 charge, so behaves like O2-
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Do another phosphate
Let's do another phosphate PO43- P 5 valence
e-4 x O 24 valence e- charge 3 valence e-
32 total electrons
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Why is phosphate 3 while sulfate is only 2?
Answer One less proton compare P (z 15) to
S (z 16)
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Take cyanide. Nonot literally!
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Formal charge is not used much in this class,
butit is described in the notes on the web.
You can get a formal charge for each atom in the
molecule. FC   Number of Protons in atom -
electrons in inner core of atom - Half the
Number of electrons in bonds - any nonbonded
electrons. Nature hates to produce charges, so
the best Lewis structure has low formal charge.

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Return of our old nemesisNonmolecular vs.
Molecular Compounds
is largely the difference between ionic and
covalent! Covalent mutual attraction to shared
ion cloud. Ionic One has electrons, the other
gave electrons.
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Liquids are a very complex and rare state of
matter.
Biggest difference cohesion. Why cohesion?
Permanent dipolese.g. water. Induced
dipolese.g. Cl2 or He (at very cold temps!)
The liquid state is remarkably rare in
particular, few planets have liquid water. Some
have liquid methane.
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Nonpolar molecules and atoms generate temporary
dipoles. The associated field travels to a
neighbor almost instantaneously, causing it to
form a complementary dipole. This leads to a weak
attraction, visible at low temperatures.
_
_
d
d
d
d
This plus charge is only a partial charge AND it
lasts just a very, very short time, but that is
long enough to induce a neighbor to generate a
charge. The two dipoles then attract, very
weakly.
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Magnet/Nail Demo
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Water is a strange, strange liquid!

• Very high melting and boiling points for such a
  light molecule (due to high polarity and H bonds)
  
• Solid density is less than liquid density. Very
  unusual!
• High heat capacity it takes a lot of energy to
  raise the temperature of water. This is important
  determining the weather and stability of ocean
  temperature, etc.
• High heat of vaporization boiling water takes
  lots of energy it really is attracted to itself!
  Can you think of social groups that are like
  this?

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Other solids lighter than their corresponding
liquid, like water.
CAUTION This is just a Yahoo Answers List!
Less Dense in Solid Form confirmed as solid
less dense than liquid gallium - 5.91 (solid)
vs 6.095 (liquid) bismuth - 9.78 (solid) vs
10.05 (liquid) germanium - 5.323 (solid) vs 5.60
(liquid) silicon - 2.3290 (solid) vs 2.57
(liquid) water - 0.917 (solid) vs 0.998 (liquid)
claimed but probably false acetic acid - 1.266
(solid) vs 1.049 (liquid) antimony - 6.697
(solid) vs 6.53 (liquid) (this "error" is
repeated in many places, inc wikipedia) Water is
not always less dense in solid form. Depending on
how the water crystals are formed, it may
actually be more dense. Examples include HDA and
VHDA.
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More about water

• High surface tension. The amount of energy
  required to expand the surface area by one unit
  of area is called the surface tension.

Figure 7.9 Surface Tension
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Hydrogen bondshow real?
Things containing -OH (e.g. CH3OH) -NH (e.g.
CH3NH2) HF
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H-bonding permanent dipoles make water very
high-boiling.
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Water Oil DemosTalc / Wax DemosSoap Demos
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Solids

• --crystalline
• a regular array of atoms or molecules exists
• We see x-ray diffraction
• examples sugar, salt, ice
• --amorphous
• atoms or molecules in no real order, yet more or
  less immobilized.
• examples glass, very rapidly cooled water or
  rapidly cooled polymers

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Metals things with distributed electrons (not
just sharedbut smeared out!)
Metals can be liquid (mercury) or solid (gold).
Usually elemental, but covalent molecular
metals and "near-metals" do exist. The nuclei
of elemental metals are usually said to be afloat
in a "sea of electrons".
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Metallic Properties all related to that sea of
electrons

• Luster--they shine!
• High electrical conductivity--use metals for
  wires.
• High thermal conductivity--cold metal will feel
  much colder than cold wood, for example. The heat
  rushes out of metal quickly. You may see someone
  walk on fiery hot coals, but not on sunbaked
  train tracks!
• Ductility and malleability metals can be drawn
  (into wire) or hammered (into leaf).
• Insolubility in water. Well...this is a tricky
  one. Metals do not dissolve with water--unless
  they react with it to produce a metal salt.

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Semiconductors are metalloids with deliberate
impurities.
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Before semiconductors, we used tubes to control
the flow of electrons.
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Transistors do the same thing as tubes, but we
can make them much smaller and at lower cost.
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The Eniac (Electronic Numerical Integrator and
Computer)
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Special types of materialsa little bit more is
said in the notes on-line.
 Supercritical fluids ... are sort of
half-gas/half-liquid substances. Gels ... are
mechanical solids made mostly from liquids!    
Aerogels   Superconductors   Liquid Crystals
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