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Now look at the central atom of CO 2 :. Two groups of four electrons each are associated with the central atom. The two groups of electrons will be 180 o from each other: the CO 2 molecule is linear. 3.3. Molecular geometry and absorption of IR radiation.

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slide2

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

slide3

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) = net change in dipole (charge distribution), so these account for IR absorption

3.4

vibrations
Vibrations
  • Do not break bonds, but they change the distribution of electronic charge.
  • a and b are stretching vibrations.
  • c and d disrupt the linearity.
  • b takes place when 4.26 µm is absorbed.
  • c and d take place when 15 µm is absorbed.
slide5

Mole: SI definition: the number equal to the number of carbon atoms in exactly 12 g of pure C-12. (SystèmInternationale)

Atomic number

Avogadro’s 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.

3.7

slide6

1 mole = 6.022 x 1023

One mole of carbon has a mass of 12.01 grams.

1 mol C = 12.01 g

If you have 36.0 g of carbon, how many moles is that?

1 mol C

36.0 g Cx

= 3.00 mole C

12.01 g C

3.7

slide7

Keep these relationships in mind:

use

molar

mass

grams

molecules

use

Avogadro’s

number

moles

Remember – the critical link between moles and grams of a substance is the molar mass

Think in terms of particles

3.7

the mole
The mole
  • The amount of substance that contains as many elementary entities as there are atoms in 0.012 kilograms (12 grams) of carbon 12
  • Avagadro’s number is a conversion factor between moles and molecules (entities) (6.022 X 1023 mol-1)
  • # atoms/mole
  • A way of standardizing for comparison
slide9
Mass
  • F=ma
  • F is force: Newtons (1kg meter/second2), which means the force required to move 1 kg of mass 1 meter/second2
  • m is mass: (1 kg=1 kilogram= 1X103grams=1000 grams)
  • v is velocity: the units are meters/sec
  • a is acceleration: the units are meters/sec2
slide13

The infrared spectrum for CO2

Wavenumber (cm-1) =10,000

wavelength (mm)

3.4

slide14

The infrared spectrum for CO2

As IR radiation is absorbed, the amount of radiation that makes it through the sample is reduced.

3.4

other gases
Other gases
  • O2 and N2 are not greenhouse gases.
  • They vibrate, but at different wavenumbers and their electronic distribution doesn’t change.
  • Next slide: the IR spectrum of water vapor.
the carbon cycle
The Carbon Cycle
  • Contributions from Nature and Humans
  • Units: Gigatonnes (Gts)
  • 1 metric ton (1 tonne)=103 kg=1000 grams=2200 lb
  • Giga=1 billion=1X109
ch 4 methane
CH4 (methane)
  • From agricultural sources: rice paddies grow with roots under water where, anaerobic bacteria produce methane
  • Animals that chew their cuds (500 L/cow/day) –cows and sheep: belching and flatulence: 73 million tonnes per year!
  • Termites: a half a tonne of termites for each person on earth! (1 tonne is over 2200 pounds)
  • Landfills
n 2 o
N2O
  • Laughing gas
  • Automobiles (coming out of catalytic converters)
  • Bacterial removal from soils in agriculture
  • Biomass burning
  • Production of nylon
  • Persists for 120 years
slide31

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

slide32

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.

3.8

slide33

Loss of Polar Ice Cap

1979

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.

2003

Perennial, or year-round, sea ice in the Arctic is declining at a rate ofnine percentper decade.

3.9

slide34

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 ocean layers, impact ocean circulation and salinity, change marine habitats, and widen shipping lanes.

2003

3.9

kilimanjaro
Kilimanjaro
  • Highest mountain in Africa.
slide37

The snows of

Kilimanjaro

82% of ice field has been lost since 1912

3.9