Chemistry from Hydrogen to Tellurium - OXYGEN

Oxygen


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? 

Chemistry from Hydrogen to Tellurium - NITROGEN

Nitrogen


The 7th element in the atomic series is Nitrogen with the chemical symbol N. Though not much talked about, Nitrogen is one of the elements we come in contact with every day. Most people think of air as being oxygen because it is the oxygen in the air that we need to breath and live. However if you got 100 "atoms" of air, 78 of them would be Nitrogen and only 21 oxygen.


So what do scientists know about Nitrogen?. Well at number 7 in the series it has 7 electrons. This means 2 in the inner shell or orbital, 2 in the second s shell and one in each of the 3 p orbitals, so nitrogen looks like this: 

  

You might like to make a model of a Nitrogen atom. All you need is 6 balloons, 2 of each of 3 colours. Inflate them and tie them together. The picture of 3 pairs of balloons tied together give a much better idea of the shape of a Nitrogen atom than my drawing.              


Nitrogen, with its 5 electrons in the outer shells has space for 3 more electrons. Because of this Nitrogen atoms are never found on their own. Two Nitrogen atoms join together  and each shares the 3 electrons in the p orbitals with the other. Scientists write this as N2. Sharing 3 electrons means they there is a triple bond between the 2 Nitrogen atoms.

So what is Nitrogen like? Well, as we know from air, at room temperature, it is a colourless, tasteless, gas. It has no smell. It is non-metalic. When cooled to -195.8°C it becomes a liquid. This liquid, known as Liquid Nitrogen is often used to cool reactions. When cooled in liquid Nitrogen, bananas become very hard and brittle and can be smashed into pieces if hit by a hammer.

Nitrogen is present in all living things. Plants are about 4% Nitrogen. Humans are about 3% Nitrogen. DNA and proteins are Nitrogen containing compounds. Plants with the help of special bacteria take nitrogen from the air and convert it into fertiliser.

So next time you breathe in, don't forget to give a little thought to this week's element of the week - Nitrogen.

Chemistry from Hydrogen to Tellurium - Carbon

Carbon


The sixth element on the periodic table is Carbon. By now you can probably guess how many electrons it has. Yes, you are right - it has 6. And its chemical symbol is C. 


Carbon is one of the most interesting elements known to scientists. It forms so many different compounds with other elements that there is a subdivision of chemistry called Organic Chemistry which is the study Carbon containing compounds. Organic chemists study the shape of Carbon containing molecules, their properties or traits, how to make them and their reactions with other chemicals.


The outer electron shell of Carbon has space for 8 electrons. Carbon has 2 electrons in its inner shell which leaves 4 in the outer shell. This means there are 4 spaces in the outer shell so each carbon atoms likes to bond or share electrons with 4 other atoms.

All of you will be familiar with Carbon and most of you use it every day. In recent weeks the elements we have been discussing don't exist on their own in nature and scientists have to extract them from other materials. Carbon is different. Carbon is a non-metal. Not only does it exist in nature, it can exist in different forms depending on how the atoms are arranged. 


In one form the Carbon molecules bond to 4 other Carbons with each atom as far from the next as possible. This gives a tetrahedral shape for 4 atoms and a 3 dimensional series of tetrahedra all joined together when there are lots of atoms. 

This form of Carbon is a clear, very hard crystal with lots of faces which reflect light and make it sparkle. We call this material Diamond.

The same Carbon molecules can also join together to form sheets of atoms. The atoms make a sheet of hexagonal rings and there are occasional links between 2 sheets to give a 3 dimensional structure. 

In this form Carbon is a black and very soft. We call this material Graphite. Graphite is used as the nibs or "lead" in pencils. Years ago real lead was used but it was found to be poisinous and was replaced by graphite. So the next time you write with pencil remember that you are rubbing layers of Carbon atoms from the nib onto your page!

Coal, soot and charcoal are also made from Carbon. In these cases the atoms are not arranged in such a regular structure 

 

In 1985 another allotrope or arrangement of Carbon atoms was discovered. It is similar to graphite but it consists of a combination of 5 and 6 atom rings. The 5 atom rings mean that the structure isn't flat so shapes like footballs and tubes can be formed. These are called Fullerenes.