I ALWAYS WANTED TO BE SOMEBODY, BUT I JUST NEVER COULD DECIDE WHO.

- ANON-

HAVE A GOAL!

THE STATES OF MATTER DIFFER FROM EACH OTHER BY DEGREE OF ORGANIZATION.

THIS IS DETERMINED, TO A LARGE EXTENT, BY THE AMOUNT OF KINETIC ENERGY (HEAT) THE ATOMS OR MOLECULES CONTAIN.

NOTE: ON EARTH, WE ARE MAINLY CONCERNED WITH THE FIRST THREE STATES.

WHEN WE THINK OF GASES, WE USUALLY THINK OF AIR – THIS BLANKET OF AIR (THE ATMOSPHERE) THAT SURROUNDS US AND THE EARTH.

GASES

THIS LAYER OF AIR THAT SURROUNDS THE EARTH IS VERY THIN.

IT’S ABOUT 30 MILES THICK – 99.9% OF THE MASS OF THE ATMOSPHERE IS LOCATED BELOW THIS ALTITUDE. ALTHOUGH, IT WOULD BE DIFFICULT TO SAY WHERE OUTER SPACE BEGAN AND THE ATMOSPHERE ENDED.

THIS AIR IS PULLED TOWARDS THE CENTER OF THE EARTH BY GRAVITY. THIS KEEPS IT FROM ESCAPING INTO OUTER SPACE.

SINCE GRAVITY IS A FUNCTION OF MASS, THE HEAVIER MOLECULES WILL BE ATTRACTED MORE THAN THE LIGHTER ONES, SO THERE WILL BE SOME DIFFERENTIATION IN COMPOSITION AS A RESULT.

FOR EXAMPLE, THERE IS VERY LITTLE HELIUM IN THE ATMOSPHERE.

Earth’s atmosphere exerts pressure on us.

At sea level, the pressure is 14.7 lb/in2.

It is due to the force of gravity on the column of air above us.

Why don’t we notice it?

IF YOU WERE ON A MOUNTAIN, WOULD THE WEIGHT OF THE AIR ABOVE YOU (AIR PRESSURE) BE GREATER THAN OR LESS THAN IT IS NOW?

PRESSURE = FORCE (weight) / AREA

OUR UNITS ARE USUALLY:

POUNDS / IN.2 (pounds per square inch)

Or

MILLIBARS

Or

INCHES OF MERCURY

1 ATMOSPHERE (pressure at sea level) = 14.7 psi = 1013.25 millibars = 760 mmHg = 29.92 in Hg

NOTE: the SI unit is the Pascal. 1 bar = 100 kPa

GAS PRESSURE IS DUE TO THE FORCE OF THE COLLISIONS OF THE GAS MOLECULES ON A SURFACE.

THE FORCE OF ONE MOLECULE WOULD BE SMALL, BUT THE FORCE OF MILLIONS CAN BE SIGNIFICANT.

A BAROMETER IS USED TO MEASURE AIR PRESSURE.

LAYERS OF THE ATMOSPHERE

BASED ON HOW THE TEMPERATURE CHANGES, THE ATMOSPHERE IS DIVIDED INTO LAYERS.

WHAT IS THE ATMOSPHERE?

THE LAYER OF GASES SURROUNDING THE EARTH AND HELD BY GRAVITY.

THE ATMOSPHERE SUPPORTS LIFE ON EARTH.

IT ABSORBS SOLAR RADIATION .

IT PROTECTS US FROM HIGH ENERGY RADIATION AND THE FRIGID VACUUM OF OUTER SPACE.

IT TRANSFERS HEAT FROM WARM AREAS TO COLDER AREAS.

THE COMPOSITION OF THE ATMOSPHERE IS:

78% NITROGEN

21% OXYGEN

1% ARGON

0.038% CARBON DIOXIDE

THIS COMPOSITION IS KEPT IN BALANCE BY LIFE ON EARTH.

IT HAS VARIED OVER GEOLOGIC TIME.

OTHER IMPORTANT GASES ARE WATER VAPOR AND OZONE.

THE AMOUNT OF WATER VAPOR WILL VARY WITH TEMPERATURE.

AS THE TEMPERATURE INCREASES, THE AIR CAN HOLD MORE WATER VAPOR.

WE EXPRESS THE AMOUNT OF WATER THAT IS IN THE AIR AT ANY GIVEN TEMPERATURE AS RELATIVE HUMIDITY.

RELATIVE HUMIDITY = (ACTUAL AMT. OF WATER IN THE AIR / MAXIMUM AMOUNT) X 100

AT A GIVEN TEMPERATURE

IF THE RELATIVE HUMIDITY IS LOW, WATER WILL EVAPORATE EASILY.

IF THE RELATIVE HUMIDITY IS HIGH, WATER WILL NOT EVAPORATE EASILY.

THE AMOUNT OF WATER VAPOR IN THE AIR VARIES WITH TEMPERATURE.

THE HIGHER THE TEMPERATURE, THE MORE WATER VAPOR THE AIR CAN HOLD.

THE NORMAL MOLECULAR FORM OF OXYGEN IS O2.

OZONE IS A LESS STABLE FORM OF OXYGEN, AND ITS FORMULA IS O3.

IN THE STRATOSPHERE, OZONE ABSORBS HARMFUL UV RADIATION.

IF THE OZONE LAYER DID NOT EXIST, LIFE AS WE KNOW IT COULD NOT EXIST.

HOWEVER, OZONE IS VERY REACTIVE.

OZONE AT GROUND LEVEL IS DANGEROUS.

GOOD UP HIGH.

BAD NEAR BY.

THERE ARE MANY OTHER WAYS THAT MAN INFLUENCES THE COMPOSITION OF THE ATMOSPHERE:

-ACID RAIN FROM OXIDES OF NITROGEN AND SULFUR DIOXIDE

-INCREASE IN CARBON DIOXIDE CONCENTRATION LEADING TO GLOBAL WARMING

-FINE PARTICULATES FROM COAL FIRED POWER PLANTS AND OTHER FIRES

-FREONS THAT DESTROY THE UPPER LEVEL OZONE LAYERS