Topics for Today Greenhouse Gases: How do they keep us warm?
Slide 2 Readings for Today 3.4 Vibrating Molecules and the
Greenhouse Effect Slide 3 Topics for Friday Climate Change: A
Global Problem? Quiz #7 (of 11)!! Slide 4 Readings for Friday 3.8
Methane and other greenhouse gases 3.10 Responding to science with
policy changes 3.11 The Kyoto Protocol on Climate Change 3.12
Global warming and ozone depletion May even bleed into Monday.
Slide 5 Announcements!!! Slide 6 Bring back your radon disks!!
Slide 7 Announcements! Nice, warm weather Please remember: Do not
wear shorts or sandals to lab!! Slide 8 Exam Regrading Same process
as Exam 1. Slide 9 Topics for Today Greenhouse Gases: How do they
keep us warm? Slide 10 Review from Monday Slide 11 Review The
Greenhouse Effect Slide 12 Review from a long time ago. Lecture 15.
( ( Slide 13 Gamma rays X-rays May ionize the molecule What happens
when molecule absorbs light? Slide 14 Gamma rays X-rays May ionize
the molecule UV light May break bonds in the molecule Slide 15
Gamma rays X-rays May ionize the molecule UV light May break bonds
in the molecule Visible light Usually doesnt do much w/out help
Slide 16 Gamma rays X-rays May ionize the molecule UV light May
break bonds in the molecule Visible light Usually doesnt do much
w/out help Infrared Important for climate change coming up!! Slide
17 Gamma rays X-rays May ionize the molecule UV light May break
bonds in the molecule Visible light Usually doesnt do much w/out
help Infrared Important for climate change coming up!! What happens
to a molecule when it absorbs IR? Slide 18 Figure 3.17 Among other
motions, this includes stretching and bending! Slide 19 Slide 20
Gamma rays X-rays May ionize the molecule UV lightMay break bonds
in the molecule Visible lightUsually doesnt do much w/out help
InfraredVibrates Molecule What happens to a molecule when it
absorbs IR? Slide 21 Q: When will IR cause a molecule to vibrate?
A: When there is a dipole moment! Slide 22 Dipole Moment: Unequal
distribution of charge! Where have we seen dipole moments before?
Slide 23 Polar Bonds: Unequal sharing of electrons in a chemical
bond. Still a covalent bond! RESULTS IN AN UNEQUAL DISTRIBUTION OF
CHARGE!! From Lecture 19 or so Slide 24 HCl -- ++ H H H N ---- ++++
++++ ++++ ---- ++++ ++++ O HH A bunch of polar molecules That is,
they have dipoles Slide 25 What about some other molecules? OCO..
Slide 26 OCO Carbon Dioxide Polar or nonpolar bonds? Slide 27 OCO..
Carbon Dioxide Polar bonds ---- ---- ++++ Slide 28 Carbon Dioxide
Polar or nonpolar molecule? OCO.. ---- ---- ++++ Slide 29 Carbon
Dioxide Nonpolar Molecule So, no overall dipole moment But CO 2 is
a greenhouse gas! Why does it absorb IR radiation? OCO.. ---- ----
++++ Slide 30 The IR can cause (or induce) a dipole moment! Slide
31 Possible Vibrations for CO 2 Think ELECTRONEGATIVITY!!! Slide 32
Symmetric Stretch Both out, both in Keeps linear shape Slide 33
Symmetric Stretch Both out, both in Keeps linear shape Slide 34
Symmetric Stretch Both out, both in Keeps linear shape Does this
induce a dipole moment? Slide 35 Asymmetric Stretch One in and one
out Keeps linear shape Slide 36 Asymmetric Stretch One in and one
out Keeps linear shape Slide 37 Asymmetric Stretch One in and one
out Keeps linear shape Does this induce a dipole moment? Slide 38
Bend Bends in one plane Loses linear shape Slide 39 Bend Bends in
one plane Loses linear shape Slide 40 Bend Bends in one plane Loses
linear shape Does this induce a dipole moment? Slide 41 Bend Bends
in another plane Loses linear shape Same as the other bend, just in
a different plane Slide 42 Figure 3.17 IR vibrations for a linear 3
atom molecule Slide 43 Bending in each plane
http://chemistry.boisestate.edu/rbanks/spectroscopy/co2vibrations.gif
Slide 44 CO 2 bending and stretching Summary Symmetric Stretch
Asymmetric Stretch Bend 1 Bend 2 Which of these is able to produce
a dipole moment? CO 2 has THREE possible ways to absorb IR!! How do
we measure this? Slide 45 Spectrophotometry Sort of Slide 46 Figure
3.15 in your Text What are wavenumbers? Slide 47 4 m = 4000 nm!
What is transmittance ? Slide 48 The opposite of absorbance!
Absorbance Slide 49 Review The Greenhouse Effect Slide 50
http://www.spaceguarduk.com/cd/dict/dictionary/infrared.htm Slide
51 Where is visible light? Higher Energy Lower Energy Slide 52
Slide 53 What happens when a molecule absorbs light? It depends on
the wavelength Slide 54 Gamma rays X-rays May ionize the molecule
UV lightMay break bonds in the molecule Visible lightUsually doesnt
do much w/out help InfraredVibrates Molecule What happens to a
molecule when it absorbs IR? Slide 55 What happens when a molecule
absorbs light? AND on the molecule. It depends on the wavelength
Slide 56 Summary For a molecule to absorb IR radiation, it must 1)
Permanently have an uneven distribution of charge (dipole) Slide 57
HCl -- ++ H H H N ---- ++++ ++++ ++++ ---- ++++ ++++ O HH Polar
molecules have dipole moments Slide 58 Summary For a molecule to
absorb IR radiation, it must 1) Permanently have an uneven
distribution of charge (dipole) OR 2) Vibrate in a way that can
CREATE an uneven distribution of charge (dipole) Nonpolar molecules
MAY or MAY NOT absorb IR radiation Slide 59 CO 2 bending and
stretching Summary Symmetric Stretch Asymmetric Stretch Bend 1 Bend
2 Slide 60 Summary For a molecule to absorb IR radiation, it must
1) Permanently have an uneven distribution of charge (dipole) OR 2)
Vibrate in a way that can CREATE an uneven distribution of charge
Nonpolar molecules MAY or MAY NOT absorb IR radiation Slide 61 Do N
2, O 2, or Ar absorb IR radiation? Slide 62 O O.. NN 1) Polar or
nonpolar molecules? 2) Can we vibrate these to produce a dipole
moment? Ar Slide 63 These molecules / atoms are NOT GHGs. 1) They
are nonpolar 2) They cannot vibrate to create an unequal
distribution of charge. Slide 64 Summary For a molecule to absorb
IR radiation, it must 1) Permanently have an uneven distribution of
charge (dipole) OR 2) Vibrate in a way that can CREATE an uneven
distribution of charge -A molecule with 3+ atoms Slide 65 How about
water? H H O.. Is water polar? But it can also vibrate!! Slide 66
Water vapor is an extremely strong absorber of IR And a very potent
GHG!! Slide 67 Water Vapor Figure 3.16 Slide 68 Figure 3.15 in your
Text CO 2 Slide 69 Water Vapor Figure 3.16 CO 2 absorbs here Slide
70 Water Vapor Figure 3.16 CO 2 absorbs here Different molecules
absorb different wavelengths! Slide 71 Does an increase in water
vapor lead to an increase in Earths temperature? Slide 72 On one
hand Slide 73 Water Vapor Figure 3.16 Slide 74 On one handOn the
other hand Slide 75 Interactions with Clouds Clouds Condensed water
on a seed particle Reflects solar radiation Slide 76 Review What is
the Greenhouse Effect? Slide 77 The Greenhouse Effect Solar
radiation Long-wave radiation Greenhouse Gases Greenhouse gases are
transparent to incoming solar radiationGreenhouse gases are
transparent to incoming solar radiation Greenhouse gases absorb the
infrared light which is emitted from the earthGreenhouse gases
absorb the infrared light which is emitted from the earth This
traps energy in the earths atmosphereThis traps energy in the
earths atmosphere Slide 78 Slide 79 About 80% of the heat emitted
from the surface is trapped in the atmosphere Slide 80 The Earths
atmosphere is about 380 ppm CO 2 The average temperature is about
59 o F Slide 81 What would the average temperature of Earth be with
no CO 2 ? About -4 o F! Slide 82 About 80% of the heat emitted from
the surface is trapped in the atmosphere Any more than this 80% is
called the enhanced greenhouse effect. Slide 83 Some people are
worried that this will lead to climate change (global warming)
Slide 84 Greenhouse gases CH 4 CO 2 H 2 O N 2 O (nitrous oxide)
CFCs and replacements Slide 85 Greenhouse gases CH 4 CO 2 H 2 O N 2
O (nitrous oxide) CFCs and replacements DONE! Slide 86 Water Vapor
Figure 3.16 Slide 87 Water Vapor Extremely strong dipole moment
(Very good at absorbing IR) Most abundant greenhouse gas (varies
from 0-4% of the atmosphere) Slide 88 Some GHGs CFCs HCFCs HFCs CO
2 CH 4 N2ON2O O3O3 H2OH2O Slide 89 What makes greenhouse gases more
potent? N2ON2O CFCs HCFCs HFCs CH 4 CO 2 CH 4 O3O3 H2OH2O Slide 90
1) Atmospheric Lifetime Slide 91 Methane Atmospheric lifetime about
10 years Removed by the hydroxyl radical we will see this reaction
Monday! Slide 92 CFCs Atmospheric lifetime >> 100 years
Destroyed in the stratosphere by UV-C Slide 93 1) Atmospheric
Lifetime 2) Atmospheric Concentration Slide 94 Concentration of CO
2 is about 370 ppm. Slide 95 Slide 96 CFC concentrations are around
0.007 ppm Slide 97 1) Atmospheric Lifetime 2) Atmospheric
Concentration 3) How efficiently can the molecule absorb IR? Slide
98 CO 2 bending and stretching Summary Symmetric Stretch Asymmetric
Stretch Bend 1 Bend 2 CO 2 has only 3 vibrations Slide 99 CFCs CFCs
have at least 10 possible vibrations!! CFCs are much more efficient
at trapping IR than CO 2. This is due to the more complicated
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