Transcript Polar vs Nonpolar DRB

versus
By Daniel R. Barnes, init 11/14/2006
But before we get started . . .
Do you remember when you read about
“resonance structures” and learned they
didn’t really resonate?
Well, galloping gertie did.
CLICK ME
http://www.youtube.com/watch?v=j-zczJXSxnw&desktop_uri=%2Fwatch%3Fv%3Dj-zczJXSxnw&app=desktop
(Thank you, Kristian Alarcon)
Page 238, Prentice Hall Chemistry:
Electronegativity
difference range
Most probable
type of bond
Example
0.0 – 0.4
Nonpolar
covalent
H—H (0.0)
0.4 – 1.0
Moderately
polar covalent
H—Cl (0.9)
1.0 – 2.0
Very polar
covalent
H—F (1.9)
>= 2.0
Ionic
Na+ Cl- (2.1)
Formula =
H2O
electronegativity
d+
d+
2.1
3.5
d-
3.5
-2.1
1.4
NOTE: Click in the grey to avoid jumping to the web page where
this picture came from.
This attraction is an example of+an “intermolecular force.”
+
It is a specific kind of attraction -called a “hydrogen bond”.
INTERMOLECULAR FORCES
d-
d-
d+
dd+
d-
d+
d+
d-
d+
d+
d+
d+
d+
d+
d-
d+
d-
d-
d+
d-
d+
d-
d+
d+
d+
d+
d-
d-
d+
d+
d+
d+
d+
d+
d+
d-
d+
d+
EXAMPLE: HYDROGEN BONDING
Attraction between
water molecules causes
“surface tension”
Hydrogen bonding between
water molecules causes
“surface tension”
Gravity  round planets/moons/stars
Surface tension  round water droplets
Surface tension 
Insect’s foot can’t get in between
water molecules 
 Insect walks on water
See how her foot makes a
dimple in the surface?
Springs help provide
tension. They pull the
skin of the trampoline
tight.
Hydrogen bonding 
solidity and form of ice crystals
Unusual “open lattice” of ice crystal 
Ice is less dense than water
H2O
H2S
+
+
water
s
-
hydrogen sulfide
Electronegativity
comparison:
Electronegativity
comparison:
oxygen = 3.5
hydrogen = 2.1
--------------------D = 1.4
sulfur =
2.5
hydrogen = 2.1
--------------------D = 0.4
+
-
+
s
-
Bonding in a water
molecule is . . .
Bonding in a hydrogen
sulfide molecule is . . .
. . . “very polar covalent.”
. . . on the borderline of
“nonpolar” and “moderately
polar”.
+
+
More polarity 
Stronger attraction
+
s
-
+
s
Less polarity 
Weaker attraction
Stronger attraction 
Molecules huddle together
but free to wander
+
Weaker attraction 
Molecules fly away
from each other
+
+
+
+
+ +
+ +
+
- +
WATER is a LIQUID
s
s
+
+
s
-
-
+
-
s
s
+
-
+
-
s
s
HYDROGEN SULFIDE
is a GAS
S
This would be a good time to read
that little passage from Fast Food
Nation about hydrogen sulfide on
page 178
. . . and now for the other one . . .
electronegativity
2.1
2.5
2.5
-2.1
0.4
Formula =
C8H18
2.5
2.1+
-
No +’s
No -’s
DISCLAIMER: C may be slightly negative & H slightly positive, but not enough to matter
No +’s
No -’s
Huh?
How do gasoline and water interact?
No minuses or plusses on the octane molecule, so . . .
No attraction, no repulsion.
. . . but . . .
+
-
. . . whatever . .
.
+
+
. . . so . . .
. . . but . . .
-
Italian Salad Dressing
Oily layer
Watery
layer
What kind of bonds are there in each
layer?
Example: C--H
Oily layer
Watery
layer
Example: O--H
As a result of polarity differences, how
are atoms charged differently?
00000000
Oily layer
Watery
layer
+-+-+-+-
Q: Why is the bond between H & O polar, whereas the
bond between H & C is nonpolar?
A: H & C have electronegativities that are almost the
same (2.1 & 2.5), whereas H & O have very different
electronegativities (2.1 & 3.5).
Q: Why does Italian salad dressing separate into two
layers?
A: It contains polar materials and nonpolar materials.
Q: Why is the oily layer on the top rather than on the
bottom?
A: Oil is less dense than water.
Water is polar, so
when you need to
wash, you often
need to add soap
to the water to
dissolve the
nonpolar
substances like
fat, grease, and oil.
?H
H
H
H
H H
H
H
HH
H
The sodium salt of a fatty acid
H
H H
H
“carbon backbone”
H
H H
H
hydrocarbon
 nonpolar covalent bonds
H
H H
H
H
H H
H
H
H
HH
H
H H
H
Hydrogen and carbon atoms are neutral
 Mixes with oily or watery materials?
?H
H
H
H
H H
H
H
HH
H
The sodium salt of a fatty acid
H
H H
H
“carbon backbone”
H
H H
H
hydrocarbon
 nonpolar covalent bonds
H
H H
H
H
H H
H
H
H
HH
H
H H
H
Hydrogen and carbon atoms are neutral
 Mixes with oily or watery materials?
O
?
O
Na+
?
Soap acts as a
“bridge” between
water and nonpolar
materials.
Soap sticks to both water AND
oily materials, so the oil and
water don’t have to separate
polar or charged  like water“hydrophilic”
HH
H
H
H H
H
H
HH
H
H
H H
H
H
H H
H
H
H H
H
H
H H
H
H
H
Soap: part metal, part fat.
Weird combo, huh?
H
HH
H H
H