At number 12 we have Magnesium with the chemical symbol Mg. Magnesium is a silvery white metal.
Magnesium is very plentiful in the universe and on earth, however like many of the other elements we have discussed, it is never found as an element on its own.
As we all know the sea is salty. This saltiness comes from various salts including Sodium Chloride the salt we are all familiar with and Magnesium Chloride which is a salt of Magnesium.
To be healthy, our bodies need Magnesium. Our bones and teeth contain Magnesium and we also need it to help digest or get energy from our foods.
The following foods are some of the sources of Magnesium - Cereals, soybean, green leafy vegetables, almonds, seeds, nuts, apples, lemon, grapefruit, seafoods, meat, milk and dairy products.
Magnesium has 12 electrons, 2 in the inner shell, 8 in the next shell and 2 in the outer shell. Again the outer shell has room for 8 so Magnesium is happy to give away these 2 "extra" electrons and form compounds with elements whose outer shells need one or two electrons to be full. You might remember way back near the start of the year we met another element with 2 electrons in its outer shell? Remember Beryllium?. It also has 2. Scientists discovered that beryllium and Magnesium behave similarly so they grouped them into a family called the Alkali Earth Metals.
Perhaps you can also remember the names of some elements whose outer shells need one or two more electrons to be full? These elements react and form compounds with the Alkali Earth Metals.
Remember oxygen? It needs 2 electrons so one oxygen combines comfortably with one Magnesium to give magnesium oxide, MgO. The reaction in which Magnesium and oxygen combine is interesting. To combine them you need to get a long thin piece of magnesium and light it. It will burn with a very bright white flame which is so bright you could damage your eyes if you look directly at it. If you were to try to use a large sheet or lump of Magnesium you would find it impossible to get it to light, even using a blow torch. Scientists have discovered that this is because Magnesium is a very good conductor of heat. No sooner than you have you heated up one corner, it has cooled itself down by passing the heat to other parts of the piece of metal. There are very interesting video clips of this. Check this one out http://boingboing.net/2010/01/23/saturday-morning-sci-13.html
We saw last week how sodium combines with 1 chlorine atom to make sodium chloride. Magnesium also forms a chloride but it needs 2 chlorine atoms as each one only has room for 1 of the two electrons magnesium has to give away.
There is a story about a farmer who was giving his cattle a drink of water. No matter what he did they refused to drink. He found however that when he washed their cuts and grazes with the same water they healed very quickly. Further investigation showed that the water had dissolved in it a Magnesium compound - magnesium sulphate MgSO4. This chemical is known as Epsom Salts and is still used by farmers on animals skins and by people in their baths to make their skin feel soft. Epsom salt makes nice needle shaped crystals and this week's experiment describes how to grow them.
Experiment
You will need:
epsom salts, water, beaker, warm water, shallow tray, spoon, ruler, adult supervision.
What to do:
Before you start examine the Epsom salt crystals carefully. Measure them, note their shape. You might even stick a few into your copy.
Place 1 or 2 spoons of Epsom salts into a beaker. Add warm water, one spoon at a time. Stir well after each spoon of water is added. Continue until all the Epsom salt has dissolved. If you did the experiment last week you should notice that you need much less water to dissolve the Epsom Aalto than you did to dissolve the sodium chloride.
Pour the solution into the shallow tray and leave in a warm dry place. After a day or 2 your crystals should begin to grow. What shape are they? How long? You should have long needle crystals varying in length from 1 to 10 cms.
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