1. Common Chemicals and their place in everyday life
Lesson 9

2. Breathe in a lungful of air, think about the billions of molecules that you are inhaling. Air is mostly nitrogen and oxygen, but you are breathing in a mixture that contains other gases as well.

3. Nitrogen (N2)
Two atoms of the element nitrogen combine to form a molecule of the gas nitrogen. Nitrogen makes up approximately 78 % of the atmosphere. It is not very reactive, which means we can breathe it in safely without causing chemical changes in our lungs.

4. However, under certain conditions, such as in a car engine, nitrogen gas reacts with oxygen to produce nitrogen dioxide (NO2), a very toxic red-brown gas. Nitrogen dioxide in low concentrations causes the yellow haze of air pollution that can be seen in some cities.

5. Argon (Ar)
Argon atoms do not combine with other atoms to form molecules. As a result, argon gas is composed of single atoms of argon. Almost all of the argon in the atmosphere has leaked out from inside the Earth. The gas is completely harmless and quite useful, especially for filling electric light bulbs and fluorescent tubes.

6. Oxygen (O2 and O3)
Atoms of the element oxygen can combine to form two different molecules. The more common of these of these contains two atoms of oxygen. This is the form that takes up about 21 % of the air that you breathe and is what we commonly call oxygen gas. Almost all organisms need oxygen to survive, as it is used in cellular respiration.

7. The less common oxygen molecule, called ozone (O3), contains three atoms of oxygen. Ozone absorbs most of the Ultraviolet radiation from the Sun.

8. Carbon dioxide (CO2) and Carbon monoxide (CO)
Two atmospheric gases contain only atoms of carbon and oxygen.
Carbon dioxide is necessary for life on earth. Carbon monoxide is extremely dangerous poisonous to animals.

9. When fossil fuels burn, the two gases produced are CO2­ and water (H2O). When there is not enough oxygen present CO is also produced. Since CO is very similar to O2 in its shape it is incredibly dangerous as it takes O2 place when it enters the lungs.

10. Combining capacities of atoms
Bond- a connection between atoms.

11. Carbon = 4 bonds
Hydrogen = 1 bond
Nitrogen = 3 bonds
Halogens = 1 bond
Oxygen = 2 bonds
Sulfur = 2 bonds
Phosphorous = 3 bonds

12. Lab Activity: Building Molecules