Magnesium is one of the lightest elements. It’s right at the beginning of the period
table and, in fact, it’s the first of the light metals that you can actually use. Lithium
and sodium react violently with water so you can’t really use them as a metal and beryllium
is fantastically poisonous so unless you are using it in the lab where you can be sure
that nobody is going to touch it, it’s useless, so magnesium is the lightest metal you can
use. So, for example, if you are trying to make mobile phones that are really light,
then you can make the frame of the mobile phone out of magnesium. You can use it for
laptops. There is a professor in Germany, who has promised to send me a laptop frame
made of magnesium, but it hasn’t arrived yet.
So another classroom classic. Normally comes along in chemistry lesson number three I guess,
time to combust a reactive metal in the air, so the reactive metal we are going to look
at is magnesium.
The other thing that is good about magnesium is that there is a lot of magnesium about
in the world, so it is not an element that is difficult to get. If you look at this periodic
table here, which is from Barcelona so it is in Catalan, the areas of these, each element
are approximately the abundance in the world. Some of the rarer elements have a slightly
bigger squares than they should do so you can read the letters, but you see magnesium
here is pretty large, so magnesium and sodium are pretty common, beryllium is much less
common, and lithium is even less common than that, so there is lots of magnesium.
Magnesium is very light, it is very reactive, very pliable metal, it is very nice, it is
easily alloyed with things like aluminium and other light metals to make very strong,
very robust materials. Used in construction, it’s used in high-performance components
of cars.
When I was a child when we got, had indigestion, we were given ‘Milk of Magnesia’. Magnesium
oxide in water which came in these really nice blue bottles, sort of white looking liquid,
didn’t taste very nice, but it was meant to be good for you, I am not sure if it was.
It is used in the hulls of ships, you know like, warships, things like that, so incredibly
strong, incredibly light but incredibly reactive if you give it enough energy. So we are going
to combust it in the oxygen and see what happens.
Magnesium as you know, burns, and one of the ways that magnesium used to be used was for
photographic flashlights, and you use bulbs like these which contain magnesium, inside
a bulb filled with oxygen. And for each photograph you had to put this on the top of the camera.
So I’ve got one here that I have taken out.
So, if you look at it, so much heat has been produced by this tiny amount of magnesium,
that it has melted the glass.
So, let’s see what happens when we light it. You can see, really fierce bright white
light that classical glow, everyone has seen this in the chemistry lab at school, fantastic
reaction.
It is one of the few metals which is meant to burn in nitrogen. In theory you can take
a piece of magnesium, set fire to it in air so its burning well and then plunge it into
nitrogen gas, and it should continue burning. I have tried this experiment lots of times
and it’s never worked. In fact for 25 years I demonstrated this experiment to my lecture
class when I was talking about nitrogen, and every time, it didn’t work, and the students
thought, the poor professor, he has been made a fool of, it hasn’t worked and they didn’t
know that it never worked and I would have been more surprised if it had done, but it
taught them a bit about the chemistry of nitrogen and magnesium.
Why did you keep doing it if it never worked?
Because it is a really good experiment, because it got such a good reaction from the audience.
Because it went wrong?
Yes!
You were playing the fool on purpose?
Yes!
So this is magnesium metal, but the magnesium metal here is not the ribbon which we normally
see in perhaps, scientific labs or perhaps in school labs, this is a very, very fine
powder of magnesium, so what we are going to do in a moment is bring on a really very
powerful torch, a gas flame and we are going to see what happens when we sprinkle a little
of this material into the flame.
Magnesium is also very important in all our lives, because magnesium is found in the green
pigments in the leaves of all plants, in chlorophyll. Chlorophyll is an organic molecule, carbon,
hydrogen and nitrogen and in the middle there is an atom of magnesium, and it is chlorophyll
which catches the sunlight and transfers it eventually to cause the reaction of carbon
dioxide and water to make all the sugars and other things in the plant. If that didn’t
happen none of us would be alive, because we all rely either directly or indirectly
on plants, to give us the energy to live.
I don’t understand completely the mechanism of photosynthesis, because the energy that
is absorbed by one molecule, is transferred to another and another one as it were along
a chain, but the magnesium is very important, if you don’t have magnesium there it is
not nearly as efficient.
Let’s light it again.