Chapter 3: Global Warming

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Chapter 3 Global Warming
We find ourselves, one way or another, in the
midst of a large-scale experiment to change the
chemical construction of the stratosphere, even
though we have no clear idea of what the
biological or meteorological consequences may
be. -F. Sherwood Rowland- quoted in Annals of
Chemistry In the Face of Doubt, The New Yorker,
9 Jun 86 A sound-bite culture cant discuss
science very well. Exactly what were losing when
we reduce biodiversity, the causes and
consequences of global warmingthese traumas
cant be adequately summarized in an evening news
wrap-up. -Barbara Kingsolver- Small Wonder, 2002
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Where we are

• Chapter 3
• lecture will focus on chapter 3 sect 1-4
• Work problems 1-13
• Due dates for paper
• Oct 19 BibliographyNov2 Outlines Nov 16
  Papers due

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nents2.gif
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The Earths Energy Balance
Greenhouse effect Our atmospheric gases trap and
return a major portion of the heat radiating from
the Earth.
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30
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3.1
5
CO2 Concentration vs. Earths temperature
3.2
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Atmospheric CO2 level on the rise
3.2
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Review How to draw Lewis structures
Draw Lewis Structures for O2 CH4 SO2 C2H4 SO4
2- 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
bonds to the atom non-bonding e-
Remember Resonance, relative lengths and bond
order!
3.3
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Valence Shell Electron Pair Repulsion Theory
Rules for VSEPR Draw a valid Lewis Structure
Ignoring double bonds, determine the number of
electron pairs around the central atom Arrange
the pairs as far apart on the central atom as
possible. Ignoring lone pairs of electrons
determine the shape of the molecules.
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Valence Shell Electron Pair Repulsion Theory
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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
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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
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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
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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
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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
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Molecular geometry and absorption of IR radiation
Molecular vibrations in CO2. Each spring
represents a CO bond. (a) no net change in
dipole - no IR absorption. (b, c, d) see a net
change in dipole (charge distribution), so
these account for IR absorption
3.4
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Molecular response to different types of
radiation
3.4