Air takes up space, has weight, is made of
a mixture of different gases, and changes with the altitude. The atmosphere is
the envelope surrounding the Earth that contains air. Air is a mixture of the
following gases: nitrogen, oxygen, argon, carbon dioxide, hydrogen, and
various other rare gases.
The percentage of carbon dioxide varies
somewhat because of the presence of vegetation. There are also traces of
ammonia, hydrogen sulfide, oxides, sulfur dioxide, and other gases. The
percentage of dry air does not vary much with location on the earth's surface.
However, the pressure of air changes greatly with the altitude. The average
pressure at sea level and 45 degrees latitude is 760 mm Hg, at 4.8 Km it is
about 400 mm Hg, at 16 Km it is about 40 mm Hg, and at 48 Km it is only 0.1 mm
- You may want students to use the
Periodic Table Placemats and find the elements abbreviation. Write the
following table on the board: