3.3

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# 3.3 - PowerPoint PPT Presentation

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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Presentation Transcript

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

3.4

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.

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

Atomic number

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

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

Keep these relationships in mind:

use

molar

mass

grams

molecules

use

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 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
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

The infrared spectrum for CO2

Wavenumber (cm-1) =10,000

wavelength (mm)

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

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
• Contributions from Nature and Humans
• Units: Gigatonnes (Gts)
• 1 metric ton (1 tonne)=103 kg=1000 grams=2200 lb
• Giga=1 billion=1X109
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
N2O
• Laughing gas
• Automobiles (coming out of catalytic converters)
• Bacterial removal from soils in agriculture
• Biomass burning
• Production of nylon
• Persists for 120 years

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.

3.8

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

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
• Highest mountain in Africa.

The snows of

Kilimanjaro

82% of ice field has been lost since 1912

3.9