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: theCO2 molecule is linear.

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

Molecular geometry and absorption of IR radiation

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.

3.7

A mole of atoms of any element has a mass (in grams) equal to the atomic mass of the element in amu.

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

Avogadro’s number is

6.022 x 1023

Atomic number

Mass number

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?

36.0 g C x 1 mol C 12.01 g C = 3.00 mole C

moles moleculesgramsusemolarmass

useAvogadro’s number

Think in terms of particles

Keep these relationships in mind:

3.7

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

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

Fig. 3.19

Box. 3.20

Box. 3.13

3.4

The infrared spectrum for CO2

Wavenumber (cm-1) = 10,000wavelength (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.

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.

Fig. 3.15

3.4

Molecular response to different types of radiation

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

The carbon cycle

3.5

Box. 3.15

Fig03.21

Box. 3.24

Page. 146.1

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

Rice Paddy

Rice Paddy

Fig03.23a Australia is studying methane’s role in climate change: floating drilling platform

Fig03.23b

N2O• Laughing gas• Automobiles (coming out of catalytic converters)• Bacterial removal from soils in agriculture• Biomass burning• Production of nylon• Persists for 120 years

Tab. 3.3

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

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 year-round, sea ice in the Arctic is declining at a rate of nine percent per decade.

Loss of Polar Ice Cap

1979

2003

3.9

Loss of Polar Ice Cap

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.

1979

2003

3.9

Kilimanjaro• Highest mountain in Africa.

Picture of Kilimanjaro in 1912

82% of ice field has been lost since 1912

The snows of Kilimanjaro

3.9