Transcript Slide 1

Chapter 3: Global Warming
The Earth’s Energy Balance
Greenhouse
effect
Our atmospheric
gases trap and
return a major
portion of the
heat radiating
from the Earth.
3.1
CO2 Concentration vs. Earth’s temperature
3.2
Atmospheric CO2 level on the rise
3.2
Review: How to draw Lewis structures
1. Determine the sum of valence electrons Draw Lewis Structures for:
CH4
2. Use a pair of electrons to form a bond O2
between each pair of bonded atoms
3. Arrange the remaining electrons to
satisfy octet rule (duet rule for H)
4. Assign formal charges
SO2
C2H4
SO42-
CO
H2SO4
N2--------------------------------NO3O3
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
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
Chargedensity
3.3
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
Valence Shell Electron Pair Repulsion Theory
Consider methane (CH4), where the central carbon
atom has 4 electron pairs around it:
Four electron pairs as far from each other as
possible indicates a tetrahedral arrangement.
A tetrahedral
shaped
molecule has
bond angles
of 109.5o.
3.3
Valence Shell Electron Pair Repulsion Theory
The legs and
shaft of a
music stand
are like the
bonds of a
tetrahedral
molecule.
3.3
The central atom (O) in H2O also has four
electron pairs around it,
but unlike methane, two electron pairs are
bonding and two are non-bonding.
The nonbonding
electron pairs
take up more
space than
bonding pairs,
so the H-to-Oto-H bond
angle is
compressed.
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
We can use the VSEPR model to allow us to
predict the shape of other molecules.
Number of electron pairs
around central atom
Shape of molecule
Bond
angle
4 electron pairs, all bonding:
CH4, CF4, CF3Cl, CF2Cl2
tetrahedral
109.5o
Triangular pyramid
about 107o
bent
about 105o
4 electron pairs, three
bonding, one non-bonding:
NH3, PCl3
4 electron pairs, two
bonding, two non-bonding:
H2O, H2S
Other predictions can be made based on
other electron pair arrangements .
3.3
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
Molecular geometry and absorption of IR radiation
Molecular vibrations in CO2. Each spring represents a C=O
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
The infrared spectrum for CO2
As IR
radiation is
absorbed, the
amount of
radiation that
makes it
through the
sample is
reduced
3.4
The infrared spectrum for CO2
Wavenumber (cm-1) = 10,000
wavelength (mm)
3.4
Molecular response to different types of radiation
3.4
The carbon cycle
3.5
Mole: SI definition: the number
equal to the number of carbon atoms
in exactly 12 g of pure C-12.
Atomic number
Mass number
Avogadro’s
number is
6.022 x 1023
A mole of atoms of any element has a
mass (in grams) equal to the atomic
mass of the element
amu.cycle
The in
carbon
3.7
6.022 x 1023
Atomic number
Mass number
One mole of carbon has a
mass of 12.01 grams;
1 mol C = 12.01 g
If you have 36.03 g of carbon, how many moles is that?
mol C = 3.0 mol C
36.03 g C x 112.01
gC
The carbon cycle
3.7
Keep these relationships in mind:
grams
use
molar
mass
moles
use
Avogadro’s
number
molecules
Remember – the critical link between moles
and grams of a substance is the molar mass.
IT’S SIMPLE – THINK IN TERMS OF PARTICLES!
3.7
CO2 emission sources from fossil fuel consumption
Deforestation contributes another 1-2 bmt/year
3.5
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
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
3.2
Loss of Polar Ice Cap
1979
2003
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.
Perennial, or yearround, sea ice in the
Arctic is declining at a
rate of nine percent per
decade.
3.9
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.
2003
Such dynamics can change the
temperature of ocean layers,
impact ocean circulation and
salinity, change marine habitats,
and widen shipping lanes.
3.9
The snows of Kilimanjaro
82% of ice field has
been lost since 1912
3.9
Intergovernmental Panel on Climate Change (IPCC)
Recognizing the problem of potential global climate 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
3.9
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, HFC’s, PFC’s, and SF6)
•Trading of emission credits allowed.
3.11
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