It was much more exciting than I thought. You see the flames.
Our first video of fluorine was a bit disappointing. There wasn’t any, just
a few bits of glassware and some funny stories. So at the moment I’m in
the office of Professor Eric Hope who is one of the Country’s specialists in
fluorine chemistry. He knows how to handle this terrific element safely. I
have no idea what to do. I’m quite excited to see what happens.
One of the things you said in that original video was, on Youtube, was
that fluorine was one of the few elements that you hadn’t seen so I
thought there are actually relatively few chemists who have seen
fluorine. So what I want to do is produce and show you elemental
fluorine. Fluorine is slowly released; you see the pressure slowly going
up.
The reason that people know about fluorine is that it is one of the really
reactive elements. It will react with all the elements of the periodic table,
except neon and helium. It will react with gold, it’ll react with silver, it’ll
react with platinum. Platinum hexafluoride is bright red as it’s a gas.
Ok so fluorine is going into the apparatus, it’s going into this tube.
Martyn, you can’t see anything can you?
I can’t see anything at all.
You can’t see anything at all, and that’s because there’s only a little
under 2 atmospheres of fluorine in there. It’s a very pale yellow colour
as a gas.
A bit disappointed but I suppose it’s like oxygen or nitrogen, you can’t
really see it. But perhaps if we condense it as a liquid then I’ll see it
properly.
Ok so now I’m going to cool this down with liquid nitrogen to -196oC. I’m
going to do it slowly. It will take a little while.
Ok Martyn, do you want to help me with this?
Yep.
So what I want to do is for you to take that flask away and I’ll slide this
one in. So if you slide it away and back up again. And there we have, oh
maybe two inches of liquid fluorine. You can go right up that, there’s no
problem with that if you want to. Just, clear a bit of condensation off
there.
Yeah I’m really surprised I thought it would be pale green and its dark
yellow. If I’d been shown it I’d thought it was liquid chlorine. But I’ve
never seen liquid chlorine either.
I’m quite pleased with that. So, basically I’ve got another fluorine
cylinder filled up from the roof with about 5 atmospheres of fluorine in it.
So this is now going to release the fluorine. And what I’ve got in this
demonstration here is just a scouring pad. It’s a metal scouring pad, iron
wool.
It burnt a hole right through the iron wool. It’s extraordinary. The iron
looks as if it’s rusted but the rusty colour is actually iron fluoride or
maybe a bit of iron oxide from the hot iron reacting with the oxygen in
the air.
Well the reason that fluorine makes such strong bonds is because it is a
small atom and the nucleus is relatively highly charged because it’s right
on the right-hand side of the periodic table but the electrons don’t shield
this nucleus. So it is very, so-called, electronegative. It attracts electrons
to itself from other elements.
I’ve changed the prop now for some just normal barbeque briquettes
which is pure carbon.
So we haven’t done anything. This is cold charcoal and cold gas, and the
gas just touching it is enough to start the fire. Think of that: just the cold
gas setting things on fire. Most chemists are really too frightened to work
with fluorine. You can’t use it in glass vessels. It doesn’t attack glass but
if the glass is a tiny bit wet and most glass has moisture absorbed into it,
then the fluorine form hydrogen fluoride and it reacts with the water and
the hydrogen fluoride just eats through the glass. So you need to use
equipment made out of metal, usually nickel, and the fluorine reacts with
the surface of the nickel, the first time you use it and then you get a
layer on the surface that protects the rest of the metal.
So this is again fluorine with sulphur. So you are going to oxidise the
sulphur, probably to sulphur tetrafluoride or sulphur hexafluoride.
Fluorine has this reputation for being very reactive and very dangerous
and something to be careful about. But aren’t their fluorine atoms in my
toothpaste?
Your toothpaste contains fluoride and, just in the same way that you can
eat sodium chloride, table salt which contains chlorine, you can use
fluorides and once the fluorine has got an extra electron, for example
from the tin in tin fluoride, which is often used in toothpaste or sodium
fluoride. It’s got what it wants and it’s not very reactive. And the way it
works with teeth is that the enamel of your teeth is a compound of
calcium called appetite, which normally the appetite in your teeth can
dissolve quite easily in acid. For example, if you eat sweets or drink
some fizzy drinks then you have enough acid to start dissolving the
surface of your teeth. But if you brush your teeth with fluoride, some of
the appetite, which contains OH groups, some of these are replaced with
fluoride and you make a material called fluoral appetite which is much
less soluble in acid so it can’t attacked so easily, so you don’t get holes in
your teeth.