WarmupFill 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

 

3

24 418 3226

3 2 4 2

0 1 1 0 0

Please leave space for two more rows below this table

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

Tetrahedral Shape

CH HH

H109.5º

4 atoms bonded to central atom

Trigonal Pyramidal Shape

NH HH <109.5º

3 atoms and 1 e- pair bonded to central atom

107°

Bent Shape

OHH

O HH <109.5º

2 atoms and 2 lone pairs bound to central atom

105o

Linear Shape2 atoms bound to central atomWith three atoms, the farthest the electron clouds can separate is 180o

C OO180º

If the central atom had a lone pair, the shape would be:

bent

Trigonal Planar Shape

3 atoms bound to central atom• The farthest you can spread

the electron pair apart is 1200

• Shape is flat

C

H

H O

120º

Fill out the table. We’ll do the first one together.

Molecule SO3 PCl3 O3 SiCl4 BeH2

Total Valence Electrons

Lewis Structure (see board) (see board) (see board) (see board) (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?

 

Trigonal planar bentTrigonal

pyramidalTetra-hedral

linear

3

24 418 3226

3 2 4 2

0 1 1 0 0

1200 1070 1050 109.50 1800

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 negativeδ+

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.”

Why do water molecules stick together?

Why do water molecules stick together?

Because they are very POLARδ– ends of O are attracted to δ+ ends of H, so hydrogen (H) bonds form

between molecules

-----

-

------

-----

-

----

--

------

------Which is stronger, the H

bonds or the polar covalent bonds?

Intramolecular forces:*Forces that hold atoms together to make a moleculeEx. covalent or ionic bond between 2 atoms

Intermolecular forces: (“Van der Waals forces”)*Weak forces that attach molecules togetherEx. dipole-dipole interactions (H-bonding), London forces

Why do water molecules stick together?

Dipole Interactions among polar molecules

MolecularPolarity

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”)

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 - δ -

CH

H Oδ+ δ -

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.

↑

δ -↓→→

δ+

δ -

δ+

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.

Polar! Drawn flat, we’d think nonpolar.

But the 3D shape tells us that the e- distribution is asymmetrical!

Cl

Cl

↓

↓

δ -

δ -

Molecular Polarity is CRITICAL in biology (just listen)Ex. Hemoglobin (protein, amino acids) carries O2 to all your cells!

normal

S.C.A.

Valine (V) is nonpolar!

Glutamic acid (E) is polar!

Mutation in the HG gene:HG isn’t the right shapeHG 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 wouldProtein chains folds differentlyO2 can’t fit in the right spot