1. Q. Are we ready for complex covalent molecules yet? A. Almost.
Astaxanthin, a member of the carotenoid family, is part of a nutritious diet—for lobsters and shrimp. These crustaceans bind astaxanthin to the protein β-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

2. So far, covalent bonding has been described as totally equal sharing
So far, covalent bonding has been described as totally equal sharing. Sometimes, sharing is or Cl H +
Cl kinda hogs
the electron.
H gets 2 (not 8
because H can’t handle 8) Cl H
Hydrogen doesn’t have to complete an octet, only a doublet.

3. Many bonds are polarized.
Electrons preferentially circulate around the chlorine atom, taking up more space there. d+ H d- Cl
Think lurid!
What about the sex life of bowling pins?

4. Magnetic Fleas

5. Covalent molecules with more than 2 atoms are slightly more complex
Covalent molecules with more than 2 atoms are slightly more complex. Example: CO2
Bonds: polar
Molecule: not polar.

6. The shape of a molecule is determined by electron-electron repulsion.
120 degrees
The first bond (gray) is normal; the second one (orange: it’s one bond in two parts) lies above & below the first bond—think of
p -type orbitals.
All there is to VSEPR theory:
How can electrons be as
far apart as possible?

7. Bungee Time: Are those C-O bonds polar?

8. 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.

9. 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.

10. 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:
120o B F F
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.

11. Let’s try methane, CH4

12. How can we spread out 4 hydrogens and their electrons?
Right idea, but we forgot an important detail. Nothing constrains the 4 electron clouds to exist in 2D!

13. Let’s illustrate this with models.

14. Tetrahedron: to draw this thing, we learn to draw a cube first
Tetrahedron: to draw this thing, we learn to draw a cube first. Then locate the lower and upper “crossed” vertices. This shape is important! H H C H
109.5 degrees in 3D gives the electrons more space than 90 degrees in 2D H

15. Water is the most amazing covalent molecule.

16. What is the shape of water?
Nonbonding e- cloud H O H
Right idea, but we forgot an important detail. Nothing constrains those electron clouds to exist in 2D!

17. Tetrahedron: to draw this thing, we learn to draw a cube first
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 H
109.5 degrees gives more
space to the electrons H

18. So water isn’t straight!
Electrons
comin’ at ya!
Electrons
Going away from you! O
Electrons in the plane
of the blackboard…
umm…screen. H H
109.5 degrees

19. It’s 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. H O
Vector addition. Break some vectors down into x and y components, then add them for practice.
*This is not a social commentary.

20.  Missouri-Yellowstone confluence
countrys/namerica/usstates/artwork/rivers/
uslayout.htm 
 Missouri-Yellowstone confluence
imageid=810&catnum=11200

21. See also: http://www.youtube.com/watch?v=RqrdcVCZ794
Let’s 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?
The purpose of this is to illustrate symmetry of forces—relating to polarity of molecules. Gotta keep trying!
See also:

22. This is a good time to introduce Concept Maps

23. Electronegative elements (Northeast elements) Suck Electrons
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
not polar
Molecule
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).

24. Happy St. Patrick’s Day (Late) Green: l ~ 530 nm

25. More complex molecules
OOPS!
OOPS!

26. Sudan I dye: a.k.a. Solvent Orange R

27. 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.

28. 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

29. Treat the molecular ion similar to an atomic one
Treat the molecular ion similar to an atomic one. Sulfate has –2 charge, so behaves like O2-

30. 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

31. Why is phosphate –3 while sulfate is only –2?
Answer: One less proton:
compare P (z = 15) to S (z = 16)

32. Take cyanide. No—not literally!

33. Formal charge is not used much in this class, but it 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.

34. Return of our old nemesis: Nonmolecular 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.

35. Liquids are a very complex and rare* state of matter.
Biggest difference: cohesion.
Why cohesion?
Permanent dipoles—e.g. water.
Induced dipoles—e.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.

36. Nonpolar molecules and atoms generate temporary dipoles
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.

37. Magnet/Nail Demo

38. 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?

39. 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 (solid) vs (liquid)
bismuth (solid) vs (liquid)
germanium (solid) vs 5.60 (liquid)
silicon (solid) vs 2.57 (liquid)
water (solid) vs (liquid)
claimed but probably false:
acetic acid (solid) vs (liquid)
antimony (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.

40. More about water Figure 7.9 Surface Tension
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

41. Hydrogen “bonds”—how real?
Things containing
-OH (e.g. CH3OH)
-NH (e.g. CH3NH2) HF

42. H-bonding & permanent dipoles make water very high-boiling.

43. Water & Oil Demos Talc / Wax Demos Soap Demos

44. 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

45. Metals: things with distributed electrons (not just shared—but 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".

46. 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.

47. Semiconductors are metalloids with deliberate impurities.

48. Before semiconductors, we used tubes to control the flow of electrons.

49. Transistors do the same thing as tubes, but we can make them much smaller and at lower cost.

50. The Eniac (Electronic Numerical Integrator and Computer)

51. Supercritical fluids ... are sort of half-gas/half-liquid substances.
Special types of materials—a 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