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.

Chemistry from Hydrogen to Tellurium - BORON

Boron

The 5^th element in the periodic table is Boron and has the chemical symbol B.

By now you will probably have noticed that each element we discuss is slightly bigger that the last. We started with Hydrogen, Atomic Number 1 and 1 electron, through Helium with 2 electrons, Lithium with 3, Beryllium with 4 and now Boron with 5.

Don’t know if you remember but Hydrogen and Helium were both gases and extremely light.

Lithium and Beryllium are both metals and solid. When describing something as a solid, liquid or a gas, scientists would always add some information about the temperature. This is because if you heat a solid you can turn it into a liquid and if you keep heating, the liquid will become a gas. This happens at different temperatures for different materials.

You will all be familiar with water – in Ireland it is a liquid, but if you lived in the North Pole you would be more used to seeing water as a solid! So the correct way to describe Lithium and Beryllium is say they are solids at room temperature. Room temperature is not a very precise term. It is the temperature that a room is at when people are comfortable in it. This is usually between 20°C and 25°C.

So what about Boron – well firstly, like Beryllium it doesn’t exist on its own. Scientists can separate it from other molecules but it is never found in nature as a clump of Boron atoms.

Almost all the elements in the periodic table can be grouped or classified as either metals or non-metals. Hydrogen and Helium are non-metals, Lithium and Beryllium metals but Boron is different. It is classified as a Metalloid. This means that it is in “no man’s land” – chemically it is somewhere in between. So sometimes it behaves like a metal and other times like a non-metal.

So far when I have drawn atoms I have always shown the nucleus in the middle with the electrons orbiting in circles around the nucleus – a bit like Saturn and its rings. Boron’s fifth electron can’t fit into the outer circular orbital as it already containing 2 electrons so is now full. The next empty orbital isn’t circular like the previous ones but it is the same shape as the number 8.

Boron Molecule

Although elemental boron is not found, boron is present in many chemical compounds. It has 3 electrons available for bonding and it usually forms the sharing, covalent type of bonds. An example of such a compound would be BF₃ – Boron triFluoride. Fluoride needs one extra electron to fill its outer electron shell so three fluoride atoms link up with one boron to make a stable compound.

It is borosilicate glass which gives pyrex its ability to be put into hot ovens without the glass shattering. Boron compounds are used in bullet proof vests and boron is also used in the computer industry to change the properties of semiconductors. Boron is found in borax, Na₂B₄O₇, which in the past was used as a cleaner.

Borax Molecule

Today and among children in particular, borax’s claim to fame is that it is the cross linking agent used to transform PVA glue into Slime.

Check out the following cool activity using the boron containing compound, Borax:

You will need: Borax, water, PVA glue, 2 beakers, weighing scales, spatula or spoon

Step 1 Dissolve 5g borax in 100mls warm water.

Step 2 To 50g PVA glue add 150mls water. Mix well. (The quantity of water required depends on how thick the PVA is so you might need to adjust the amount of water needed).

Step 3 While stirring the PVA solution gradually add small amounts – say 1 teaspoon at a time, of the borax solution you prepared in step 1. Continue stirring and adding borax solution until the PVA turns to a rubbery slime.

Step 4 Take the slime out of the container and have fun playing with it.

Chemistry from Hydrogen to Tellurium - BERYLLIUM

Beryllium

Here we are at week four and the turn of Beryllium, with its chemical symbol Be. What a nice name - I love the sound of it - so exotic. When it was first discovered, because of its sweetness it was called Glucinum - a name which came from glucose. Tasting chemicals is a really bad idea - in the past lots of chemists have died as a result of tasting and even working carelessly with chemicals which turned out to be poisonous. Beryllium is no exception - its salts are toxic and should never be tasted.

The name Beryllium came from the Beryl, the mineral name of a range of gemstones which contain Beryllium and include Emeralds and Aquamarine. Beryl is a molecule made up of Beryllium, Aluminium, Silicon and Oxygen atoms

Emerald Aquamarine

Aquamarine is a relatively common gemstone and is said to be the birth stone for March.

Emerald is quite rare and therefore a valuable gemstone. It is the birth stone for May.

If any of you have earrings, rings or bracelets with aquamarine or emeralds in them then you have a few Beryllium atoms!

Beryllium is quite rare. It doesn't exist naturally on its own but when scientists separate it from Beryl it is a strong gray metal. Because Beryllium metal doesn't get much bigger or smaller when it is heated or cooled it is ideal for using on planes and rockets.

Beryllium is number 4 on the periodic table and has 4 electrons orbiting its nucleus. These 2 pairs of 2 electrons make it quite happy so it is not a reactive element. It does sometimes give away its outer 2 electrons to atoms of elements such as chlorine which are very keen to fill up their outer electron shell.

From Hydrogen to Tellurium - LITHIUM

Lithium

Lithium is the third element on the periodic table. It is not as famous as either hydrogen or helium so you might not have heard of it before. Being the third element, it has 3 electrons, 2 in the inner circle and one on its own in an outer orbit.

Lithium is quite happy to give away this outer electron and because of this scientists say that it is reactive. It gives away its outer electron to elements such as Hydrogen which need one additional electron to fill their outer shell of electrons. When a Lithium atom gives an electron to a hydrogen atom a new compound called Lithium Hydride is formed. There is no sharing of electrons involved. Scientists call this type of bonding ionic bonding.

I think of Lithium as being like a family with 3 children (electrons). The younger 2 are happy to stay near their parents (the nucleus). The older child or electron likes to go on sleepovers and often stays away for long periods of time.

The bonds in this type of compound are different to those discussed when we were talking about hydrogen joining with another hydrogen atom to make H2. In H2 both hydrogen atoms share the 2 electrons. Scientists call this a covalent bond.

The covalent bonds of Hydrogen remind me of 2 families with one child each living next door to each other. The children play together, moving from house to house, garden to garden. It is almost as if both families have 2 children.

Other elements which need one extra electron are Fluorine and Chlorine and these also form ionic bonds with lithium. We will be talking about these elements during weeks 9 and 17 respectively.

So what is Lithium like? Well, it is a metal and a solid, but unlike most metals it is very light - it is so light it can float on water. However if you put it on to water it will start to react - it will dart around and bubbles of hydrogen will be formed. As well as being very light it is soft and can be cut with strong scissors.

And its uses - the most common use for Lithium is in batteries.

From Hydrogen to Tellurium - HELIUM

Helium


Having talked about Hydrogen last week, this week it is the turn of Helium. This well known gas is best known for its ability to make balloons float and for making your voice squeaky.


How does it make balloons float? Well, like hydrogen, Helium is one of the lightest molecules. It is lighter or less dense than air and so if you fill a balloon with Helium the balloon will rise up through the air and float. A balloon containing hydrogen would also float in air but Helium has a major advantage over hydrogen - Helium is much safer. Hydrogen with its single electron is very reactive and a tiny spark causes it to burn in air to produce water. As we saw last week, when controlled in a rocket's engine this is a very useful reaction. It is much more difficult to control in a balloon. In the past Hydrogen was used to lift balloons and air ships and was in use until the Hindenburg Disaster in 1937 when the hydrogen balloon carrying an airship burst into flames killing many of the passengers.


So why is Helium so much safer than hydrogen? Well the reason Helium is number 2 on the periodic table of elements is because it has 2 electrons. An atom with 2 electrons is content to stay like that and has no need to share, give away or look for extra electrons. A Helium atom reminds me of a family with twins. Just like twins, the 2 Helium electrons are happy with their own company. This means that Helium is not reactive or as scientists would say - inert.


Could Helium balloons be used to lift a person? There are various reports of people using Helium balloons to fly. A plane is reported to have contacted the control tower reporting a man on a deckchair floating in the flight path being lifted by Helium balloons. Apparently he kept attaching balloons to the chair and eventually it took off. He was unable to reach the balloons to burst them and was floating, unable to return to earth when the pilot saw him. He was rescued by a helicopter.
Others have not been so lucky and have drifted off never to be seen again.


I reckon it would take a lot of Helium balloons to lift a person - According to our experiments each balloon can lift approx 5g. At that rate you would need 200 balloons to lift 1kg! No matter how many balloons you would need do not try it. It is definitely one of those experiments which you MUST NOT try at home.