But of course it's not just the air that they could react with, there are other things as well.
It could also react with the water and this is what we're going to show now.
The way you may have seen this in previous demonstrations, they normally throw the
metal into some water,
but there's all sorts of problems with this because the metal may have grease on it,
it may be contained in glass ampuole if it's a really reactive metal like
caesium or rubidium.
So we're going to do this rather differently, we're going to add the water
to the metal. We're going to use the same quantity
of metal every time and not the same mass
but the same number of atoms so Marc has very carefully counted out
the number of atoms and he's got the same amount each time
so we're going to start off with lithium and I'm going to add the same quantity of water
every time as well, we're going to add 10 ml of water
to our metal. I'm going to take the top off, at the moment they're under argon
so there's no reaction of metal with the air,
argon is heavier than air and it's just sitting in the tube protecting the metal
from the air and we're just going to add some water. So this is lithium, you can see
that it's bubbling rather nicely,
it's forming hydrogen gas and in fact we can see the chemical equation for
the reaction, it's the same chemical equation for all of the elements, we have the metal
reacting with water to form the metal hydroxide
and releasing hydrogen, hydrogen gas, so every time it's the same equation.
But what we're trying to do now is see if we can tell the difference
between the reactivities of the different metals. So out with the lithium,
in with the sodium. Now again,
it's the same quantity of metal,
but does it react anymore vigorously?
I'm going to add the same quantity of water.
Right, so the sodium certainly a lot more violent than the lithium.
In fact it caught fire. Notice the yellow colour, this is the colour
characteristic of excited sodium atoms so the sodium was clearly having a good time there.
Right, potassium.
Again, the same quantity, the same number of atoms. We're trying to keep everything
as controlled as possible.
The same quantity of water and just as an added safety precaution I think I'll put this on.
So potassium now, and water.
Getting more vigorous.
Okay, maybe we can, yes that's a good idea.
We'll just remove some of the smoke so you can see the next one more clearly.
Now some rubidium. We had an extra blanket I think
Here's the rubidium in the tube here, we can see the rubidium metal
under a blanket of argon.
Again, it's exactly the same quantity, every time we're using the same quantity.
It's now rubidium, same quantity of water.
Beautiful blue colour.
That's the colour of the rubidium flame remember. We need to wait for that to go.
Okay we just wait for this to clear because this is a one-off experiment here.
The amount of caesium that we're using is five grams
and it cost several hundred pounds so here is our caesium
and again if we just show this on the camera there.
So there's quite a bit of the metal down in the bottom of the tube and again
it's under a blanket of argon so it will not react with argon gas.
When I take the stopper off it will not be reacting with the air because the
argon is heavier than air and so that will protect it until
it comes into contact with the water and we've used the same quantity
of every metal here. The same number of atoms.
Here is our water
and there we go. Not bad.
I'm pleased that one's over.
So actually caesium though
it is the most reactive, there's no doubt it's the most reactive
of all of the metals and reacts very, very quickly.
It's also heavier than water.
Both rubidium and caesium sink to the bottom of water.
So that's one of the reasons it reacts very quickly, but I always think that the best reaction
actually is with sodium and water, this is my favorite,
because I think the sodium has more of a chance to sort of
build up the tension and heat up,
it's much more interesting. So we're going to try some more sodium now on a slightly larger scale
in the tank here.
Notice the amount of francium left, it's still decreasing, there's not a lot left now,
so that's why we're not going to be looking at any francium.
Here is our sodium, going to drop this into the tank
and run away.
Can't see where it is, oh, there we go.