November 16, 2009
• C h a p t e r 8
•
Homework posted
•
Lab Notes
•
Today’s Topic:
Bond Properties (Sec. 8.4- there is no 8.3!)
Electron Distribution in Molecules (8.5)

Rules for Drawing Lewis Structures
1.
2.
3.
4.
5.
6.
7.
Write the skeletal structure
Add up the total # of valence electrons
Draw a bond between the central atom and each surrounding atom
Add lone pairs to the outer atoms to complete their octets
Add remaining electrons to central atom
If central atom does not have an octet, “borrow” electrons from other atoms (make double/triple bonds)- DO NOT
ADD ELECTRONS (F and Cl do not form multiple bonds;
C, N, O, P, and S do)
Sometimes you can’t complete an octet (B and Be)

Did you try this at home? Here’s the answer…
__# electrons__
C = 4
H = 2 x 1 = 2
Cl = 2 x 7 = 14
Total = 20

 CHCCHCH
2
Organic Structures

What can we do with Lewis Structures?
 Bond Properties
1.
2.
3.
4.
Polarity
Bond Order
Bond Length
Bond Energy

Imagine they are nuclei
Bond Types
Imagine this is a valence electron
Nonpolar Covalent
Polar Covalent
Ionic

Polarity
 Electronegativity- The ability of an atom involved in a bond to attract electrons to itself

Orbital energy, effective nuclear charge

Polarity
 Electrons drawn closer to the more electronegative atom

Trend in Electronegativities

Bond Character: From Covalent to Ionic

In a C-O bond, which element will have a greater concentration of electron density?
1.
2.
3.
Carbon
Oxygen
Neither, they will share the electrons equally
80%
15%
5%
3 1 2

Bond Order
 The number of bonding electron pairs between two atoms

 Atom size
 Bond order
Bond Length

1.
4.
5.
2.
3.
H - H
H - Cl
Cl - Cl
Cl - Br
Br - Br
Which bond is the longest?
19%
16%
12%
8%
45%
1 2 3 4 5

Which bond is the shortest?
1.
2.
3.
4.
N-N
N=N
N  N
All are the same length
20%
40%
36%
1
3%
2 3 4