Number 8 on the periodic table of elements is Oxygen with the chemical symbol O. Oxygen is a clourless gas with no smell. Most people have heard of it because it is essential for life. Oxygen is produced by plants in a process called photosynthesis. Photosynthesis means making something using light. When light shines on plants and there is water and carbon dioxide present the plants absorb the water and carbon dioxide and convert it into glucose and Oxygen. The Oxygen is then released into the air and as we saw last week when discussing nitrogen, air is 21% Oxygen. This means that if you had 100 "air atoms", 21 of them would be Oxygen.
Being number 8 on the periodic table means that Oxygen has 8 electrons, 2 in the inner shell and 6 in the outer one. More important is the fact that it has space for 2 more electrons in that outer shell to make it full. This means that Oxygen is keen to borrow or share 2 electrons with other atoms. Because of this need for extra electrons, Oxygen atoms are not found on their own, but instead joined in pairs, in much the same way as hydrogen which we discussed in week 1.
O2 molecule.You will also be familiar with another Oxygen containing compound - Water. Water, or H2O is made up of 1 Oxygen atom and 2 hydrogens.
As well as people and animals not being able to live without Oxygen, fire cannot burn without it either. This is why when you remove the Oxygen from a fire by covering the fire with a fire blanket, the fire goes out.
Experiment to remove oxygen from the air.
You will need adult supervision / help, a breakfast bowl, a nightlight, water, matches or a lighter and a drinking glass
Put about 1 cm of water into the breakfast bowl.
Float the candle on the water.
Light the candle.
Place the upturned drinking glass over the candle.
After a few seconds the flame will go out. The air trapped in the drinking glass has had its oxygen removed.
Look at what happens to the water. Can you explain this?
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