They give you fever When you kiss them Fever if you live, you learn

They give you fever When you kiss them Fever if you live, you learn

They give you fever
When you kiss them
Fever if you live, you learn
Fever, till you sizzle
What a lovely way to burn
Fever - Peggy Lee (Little Willie John, Elvis, Madonna,
the Bobs, Ella Fitzgerald, Beyonce, the Kingsmen, Buddy
Guy, Michael Buble, Joe Cocker . . .)
"The planet has a fever." -Al Gore
Greenhouse effect
Chemical concepts
•
•
•
•
Molecular shape
Polar bonds / polar molecules
Vibrations
IR interaction with molecules
Shape, the simplest case
H
H
O
O
N
N
Cl
Cl
H
Cl
• Diatomic molecules
are linear
• 2 points define a line
Molecular shape
• VSEPR - Valence Shell
Electron Pair Repulsion
• Electrons act in pairs
(bonds or pairs of nonbonded electrons), or
groups of pairs (double
and triple bonds)
• These repel each other
2 bonds (or sets of bonds)
• The furthest apart 2 groups
can get is 180 degrees
• Linear
F
Be F
Cl
O
C
H
O
Mg Cl
C
N
3 bonds (or sets of bonds)
• The furthest apart 3 groups
can get is 120 degrees
• Trigonal planar
H
H
Cl
O
B
Al
C
H
Cl
Cl
H
H
4 bonds
• The furthest apart 4 groups
can get is 109.5 degrees
• Tetrahedral
H
H
C
H
H
H
H
C
H
H
Unshared electrons? NH3
•
•
•
•
Electron pairs (lone pairs) also repel
NH3 has 3 bonds and 1 lone pair
These are all at ~109.5 degrees (107.8)
The shape, though is named after
the location of the atoms
• Trigonal pyramidal
H
N
H
H
H
N
H
H
Unshared electrons? H2O
• H2O has 2 bonds and 2 lone pairs
• These are all at ~109.5 degrees (104.45)
• The shape, though is named after
the location of the atoms
• Bent, angular
H
O
H
H
O
H
H
O
H
Unshared electrons? O3
• O3 has 2 sets of bonds and 1 lone pair
• These are all at ~120 degrees (116.8)
• The shape, though is named after
the location of the atoms
• Bent, angular
O
O
O
Electronegativity
• How much an element pulls on the electrons
Most
Least
Electronegativity: a tug of war
A
!
A
!
Covalent
A
B
Polar covalent
A
Z
Ionic
Polar bonds, polar molecules
• In some molecules, the
bonds are non-polar, so
the molecule is nonpolar
• In some molecules,
polar bonds cancel out,
so the molecule is nonpolar
• In some molecules,
polar bonds add up, so
the molecule is polar
H
O
H
H
C
O
O
H
Molecular vibrations
• Ball and spring model of bonding
• Stretching, bending, more complex
modes
Harmonic motion
• Vibration energy depends on force constant
of the spring and masses of the balls
• This equates to bond and element types
• Different vibration energies correspond to
different light energies
• Infrared light - lower energy than UV or Vis
IR active vibrations involve a
change in polarity
O
O
non-polar
N
N
non-polar
O
O
IR
inactive
non-polar
N
N
non-polar
IR
inactive
• O2 and N2 do not absorb IR!
O C O
O
C
O
non-polar
non-polar
O C O
OC
non-polar
O C O
polar
C
O
O
non-polar
polar
O
IR inactive
IR active
IR active
• CO2 (and H2O and CH4) do absorb IR!