1. Warmup
Fill out the table below. Make sure to draw the Lewis structure in pencil! Try your best!
Molecule
SO3
PCl3 O3
SiCl4
BeH2
Total Valence Electrons
Lewis Structure
# of Atoms Attached to Central Atom
# of Lone Pairs Attached to Central Atom 24 26 18 32 4 3 3 2 4 2 1 1
Please leave space for two more rows below this table

2. We’re going to keep it simple…..this gets much more complicated

3. Tetrahedral Shape
4 atoms bonded to central atom H
109.5º C H H H

4. Trigonal Pyramidal Shape
3 atoms and 1 e- pair bonded to central atom N H H
<109.5º H
107°

5. O H O H H H Bent Shape 2 atoms and 2 lone pairs bound to central atom
<109.5º H H
105o

6. O C O Linear Shape 2 atoms bound to central atom
With three atoms, the farthest the electron clouds can separate is 180o
If the central atom had a lone pair, the shape would be:
180º
bent O C O

7. H C H O Trigonal Planar Shape 3 atoms bound to central atom
The farthest you can spread the electron pair apart is 1200
Shape is flat H
120º C H O

8. Fill out the table. We’ll do the first one together.
Molecule
SO3
PCl3 O3
SiCl4
BeH2
Total Valence Electrons
Lewis Structure
(see board)
# of Atoms Attached to Central Atom
# of Lone Pairs Attached to Central Atom
Molecular Shape Name
What is the angle between the bonds? 24 26 18 32 4 3 3 2 4 2 1 1
Trigonal planar
Trigonal pyramidal
Tetra-hedral
linear
bent
1050
1800
1200
109.50
1070

10. Why do water molecules stick together?
Remember how H and O have an electronegativity difference of 1.4? The bond between H and O is polar covalent.
The more EN atom (O) will get the e-’s for a greater amount of time and thus be slightly more negative δ- δ+ δ- δ+ δ+
Net Dipole/Dipole Moment: this is actually very complicated and involves magnetic fields and calculus. For our purposes, consider it to be “an uneven electron (negative charge) distribution throughout a molecule.” 16

11. Why do water molecules stick together? Because they are very POLAR
δ– ends of O are attracted to δ+ ends of H, so hydrogen (H) bonds form between molecules
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Which is stronger, the H bonds or the polar covalent bonds?
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12. Why do water molecules stick together?
Intramolecular forces:
*Forces that hold atoms together to make a molecule
Ex. covalent or ionic bond between 2 atoms
Intermolecular forces: (“Van der Waals forces”)
*Weak forces that attach molecules together
Ex. dipole-dipole interactions (H-bonding), London forces

13. Dipole Interactions among polar molecules
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-
d+ d-

14. H C H O Molecular Polarity
δ +
polar molecules have one end with a - charge and the other a + charge; there is a net dipole (“dipole moment”)
diatomic molecules with a polar bond, bent and trigonal pyramidal shapes are usually polar
δ -
δ -
CO2 has 2 polar covalent bonds. The O’s are more EN than the C, so each O hogs the shared e- cloud from the C.
The right AND left ends of the molecule have a slightly negative charge.
Entire molecule is symmetrical, nonpolar, and there is NO net dipole! (no “dipole moment”) H C δ+ H O
δ -

15. Is CCl2H2 polar or nonpolar? Explain.
δ - δ+ ↓ ↓
δ - δ+ → → ↑
δ - ↓ δ+ Cl
δ -
If we were to replace one H with a Br atom (bromomethane), the Br atom would attract the shared pair of electrons more strongly than the H opposite to it. Thus, the molecule becomes slightly polar.
Is CCl2H2 polar or nonpolar? Explain.
Methane has 4 equal C-H bonds. The symmetrical distribution of the polar bonds in the molecule cancels out the effects of the bond polarity, methane remains nonpolar.
Polar! Drawn flat, we’d think nonpolar. But the 3D shape tells us that the e- distribution is asymmetrical!

16. Molecular Polarity is CRITICAL in biology (just listen) Ex
Molecular Polarity is CRITICAL in biology (just listen) Ex. Hemoglobin (protein, amino acids) carries O2 to all your cells!
Mutation in the HG gene:
HG isn’t the right shape
HG molecules can’t distribute O2 to cells !!!!!!!!
Mutation causes valine (nonpolar) to be where glutamic acid (polar) should be.
Valine doesn’t interact with neighbors the same way as glutamic acid would
Protein chains folds differently
O2 can’t fit in the right spot
normal
Glutamic acid (E) is polar!
S.C.A.
Valine (V) is nonpolar!