Chapter 3: Global Warming

1
Chapter 3 Global Warming
2
The Earths Energy Balance
Greenhouse effect Our atmospheric gases trap and
return a major portion of the heat radiating
from the Earth.
3.1
3
CO2 Concentration vs. Earths temperature
3.2
4

Atmospheric CO2 level on the rise
3.2
5

Review How to draw Lewis structures
Draw Lewis Structures for O2 CH4 SO2 C2H4
SO42- CO H2SO4 N2---------------------------
-------NO3- O3
1. Determine the sum of valence electrons

• Use a pair of electrons to form a bond
• between each pair of bonded atoms

• Arrange the remaining electrons to
• satisfy octet rule (duet rule for H)

4. Assign formal charges
Formal charge of v.e. of non-bonding e-
½ bonding e- or, F.C. of v.e. of bond
s to the atom non-bonding e-
Remember Resonance, relative lengths and bond
order!
3.3
6
Representations of methane
CH4 molecular formula does not express
connectivity

Structural formulas show how atoms are connected

Lewis structures show connectivity
This Lewis structure is drawn in 3-D
Space-filling Charge-
density

3.3
7
The 3-D shape of a molecule affects ability to
absorb IR radiation.
Valence Shell Electron Pair Repulsion Theory
Assumes that the most stable molecular shape has
the electron pairs surrounding a central atom as
far away from one another as possible
3.3
8
Valence Shell Electron Pair Repulsion Theory
Consider methane (CH4), where the central carbon
atom has 4 electron pairs around it

A tetrahedral shaped molecule has bond angles of
109.5o.
Four electron pairs as far from each other as
possible indicates a tetrahedral arrangement.
3.3
9
Valence Shell Electron Pair Repulsion Theory
The legs and shaft of a music stand are like the
bonds of a tetrahedral molecule.
3.3
10
The central atom (O) in H2O also has four
electron pairs around it,
The non-bonding electron pairs take up more space
than bonding pairs, so the H-to-O-to-H bond angle
is compressed.
but unlike methane, two electron pairs are
bonding and two are non-bonding.
The electron pairs are tetrahedral arranged, but
the shape is described only in terms of the atoms
present water is said to be bent shaped.
3.3
11
We can use the VSEPR model to allow us to predict
the shape of other molecules.
Other predictions can be made based on other
electron pair arrangements .
3.3
12
Now look at the central atom of CO2
Two groups of four electrons each are associated
with the central atom.
The two groups of electrons will be 180o from
each other the
CO2 molecule is linear.
3.3
13
Molecular geometry and absorption of IR radiation
Molecular vibrations in CO2. Each spring
represents a CO bond. (a) no net change in dip
ole - no IR absorption. (b, c, d) see a net cha
nge in dipole (charge distribution), so
these account for IR absorption
3.4
14
The infrared spectrum for CO2
As IR radiation is absorbed, the amount of
radiation that makes it through the sample is
reduced
3.4
15
The infrared spectrum for CO2
Wavenumber (cm-1) 10,000
wavelength (mm)
3.4
16
Molecular response to different types of
radiation

3.4
17
The carbon cycle
3.5
18
Mole SI definition the number equal to the
number of carbon atoms in exactly 12 g of pure
C-12.
Atomic number
Avogadros number is 6.022 x 1023
Mass number
A mole of atoms of any element has a mass (in
grams) equal to the atomic mass of the element in
amu.
The carbon cycle
3.7
19
6.022 x 1023
Atomic number
One mole of carbon has a mass of 12.01 grams
1 mol C 12.01 g
Mass number
If you have 36.03 g of carbon, how many moles is
that?
1 mol C
36.03 g C x
3.0 mol C
12.01 g C
The carbon cycle
3.7
20
Keep these relationships in mind
use molar mass
molecules
grams
use Avogadros number
moles
Remember the critical link between moles and
grams of a substance is the molar mass.
ITS SIMPLE THINK IN TERMS OF PARTICLES!
3.7
21
CO2 emission sources from fossil fuel
consumption

Deforestation contributes another 1-2 bmt/year
3.5
22
Amplification of Greenhouse Effect
Global Warming
What we know
1. CO2 contributes to an elevated global
temperature.
2. The concentration of CO2 in the atmosphere has
been increasing over the past century.
3. The increase of atmospheric CO2 is a
consequence of human activity.
4. Average global temperature has increased over
the past century.
3.2
23
What might be true
1. CO2 and other gases generated by human
activity are responsible for the temperature
increase.
2. The average global temperature will continue
to rise as emissions of anthropogenic greenhouse
gases increase.
3.9
24
3.2
25
Loss of Polar Ice Cap
NASA Study The Arctic warming study, appearing
in the November 1 2003 issue of the American
Meteorological Society's Journal of Climate,
showed that compared to the 1980s, most of the
Arctic warmed significantly over the last decade,
with the biggest temperature increases occurring
over North America.
1979
2003
Perennial, or year-round, sea ice in the Arctic
is declining at a rate of nine percent per
decade.
3.9
26
Loss of Polar Ice Cap
1979
As the oceans warm and ice thins, more solar
energy is absorbed by the water, creating
positive feedbacks that lead to further melting.
Such dynamics can change the temperature of ocea
n layers, impact ocean circulation and salinity,
change marine habitats, and widen shipping lanes.
2003
3.9
27
The snows of Kilimanjaro
82 of ice field has been lost since 1912
3.9
28
Intergovernmental Panel on Climate Change (IPCC)
Recognizing the problem of potential global clim
ate change, the World Meteorological Organization
(WMO) and the United Nations Environment
Programme (UNEP) established the
Intergovernmental Panel on Climate Change (IPCC)
in 1988. It is open to all members of the UN and
WMO.
3.9
29
3.9
30

• Kyoto Protocol - 1997 Conference
• Intergovernmental Panel on Climate Change (IPCC)
  certified the scientific basis of the greenhouse
  effect.
  
• Kyoto Protocol established goals to stabilize and
  reduce atmospheric greenhouse gases.
  
• Emission targets set to reduce emissions of six
  greenhouse gases from 1990 levels.
  
• (CO2, CH4, NO, HFCs, PFCs, and SF6)
• Trading of emission credits allowed.

3.11
31
The Kyoto Protocol, an international and legally
binding agreement to reduce greenhouse gases
emissions world wide, entered into force on 16
February 2005.
Notable country who has not signed
3.11