Lithium is the lightest metal.
We all know that sodium is pretty light as a metal.
If you drop it onto water and forget the reaction, it floats.
You can see the orange sodium flame.
Oh, It's on the camera.
Of course, lithium will do the same, though, there are differences which I will show you in a minute.
But what I wanted to see was whether we could demonstrate how much lighter lithium was than sodium.
We've never tried this experiment before, but I asked Neil, our technician, to drop
a piece of sodium and a piece of lithium of approximately the same size, at the same time
into beakers of hexane. Hexane is similar to gasoline, or petrol, and when he dropped them, it was really striking
The sodium sank like a stone, because gasoline is much less dense than water. But lithium bobbed around
like a little boat. If you look carefully, they both started bubbling,
because we didn't use dry hexane, and both samples of hexane contained just a little bit of water, that
started reacting. And of course, that prompted Neil to want to drop the lumps of metal into real water.
So we tried the experiment again, dropping lithium and sodium into water.
Of course, this time, both of them floated.
But lithium is less reactive towards water than sodium.
It's a smaller atom, the electrons are more tightly held, and the reaction is slower.
With the sodium, it was really quite surprising, it went off with a real bang,
and the beaker ended up in the back of the fume cupboard.
And the sodium was gone. And the lithium quietly buzzed around on the surface of the water.
And when Neil encouraged it with a flame, we got a beautiful red colour, the characteristic flame colour, of lithium.
The other experiment we tried was burning lithium in air, and comparing it with burning lithium in nitrogen.
N2 has the strongest bond between any two atoms of the same sort in the periodic table, so you need
a lot of energy to break them apart. Because lithium is small, it can form very tight bonds with nitrogen,
and so I read frequently that lithium will burn in nitrogen. So I persuaded Neil to set fire to some lithium
and it burned really brightly in air,
and then poured liquid nitrogen into a beaker, to fill it up with nitrogen gas.
Nitrogen boils at -200C or -196C, so the gas was pretty cold in the beaker. And then he plunged the burning
lithium into the beaker. Now here, there was a difference of opinion between me and
Neil, I thought the reaction was a great success,
Neil was a bit disappointed,
because the lithium just glowed red.
But what I saw, was that this is not a very big piece of metal
being plunged into really cold gas
and it kept on glowing red. On and on and on,
whereas if it had just been put out because it wasn't reacting with nitrogen
it would have lost its color very quickly. So I felt that it was a
reasonable demonstration.
I've tried to do the same demonstration with magnesium which is also meant to
burn in nitrogen,
I demonstrated it for 25 years, to successive generations of students and
didn't work once. I knew it wouldn't work but every time the students thought:
"Stupid professor! Doesn't work!"
Lithium is used for treating bipolar disorder,
sometimes called manic depression. This is a very distressing disease which is
caused by imbalance of chemicals in the brain which causes people sometimes to
be really manic and other times so depressed that they can't get out of bed.
The application which you use probably most often for lithium is in factories.
This is not a new idea I found an old scientific american from 1967.
And inside there is an advertisement here, with the picture of Edison's desk. On this desk
when he died was a large can of lithium.
This is an advertisement from a company that sells lithium or sold lithium, in those days.
The reason that Edison had lithium on his desk was that he
realized it could potentially make really good batteries.
[Brady] Is that the known reason, or is that just what Foote mineral company is suggesting?
I think that's what they're suggesting.
And since he didn't make lithium batteries, perhaps we'll never know.
So there's one final and the important application of lithium which is in
making hydrogen bombs.
Let me just remind you that an atom bomb is formed by atoms
usually of uranium that could also be plutonium, splitting apart.
This a called fission bomb, a hydrogen bomb is inherently different.
The Atomic Energy Commission and the Department of Defense have conducted important
tests of an experimental device based on a thermonuclear principle.
Bits come together. So two atoms, for example, two deuterium atoms.
But what is deuterium?
I was coming to that. An atom of this kind of hydrogen has the simplest
nucleus known. But hydrogen exists in two other isotopic forms: deuterium, which
has a neutron in addition to the proton, and tritium, which has two neutrons and one proton.
Atoms of hydrogen with mass two, rather than mass one,
come together to form an atom of helium. The first hydrogen bombs that
were made, and they really ought to be called deuterium bombs not hydrogen bombs,
involved liquid deuterium. And so the bomb really looked like a small
chemical factory because they were big tanks of liquid deuterium and nobody
could imagine carrying this on an airplane for actually bombing.
This is the first full-scale test of a hydrogen device.
If the reaction goes, we are in the thermonuclear era.
five, four, three, two, one..
The breakthrough came when it was realized that you could use the compound of
lithium and deuterium this is lithium deuteride, LiD.
Which is chemically the same as LiH,
but with a heavier isotope. What happens with that sort of bomb is that you
trigger it with an atom bomb that produces a lot of neutrons and the
neutrons turn some of the lithium atoms into tritium, hydrogen of mass three, and
then the deuterium and the tritium fuse together giving out energy.
Lithium deuteride is a solid which is stable at room temperature. In principle
you could make lithium tritide, LiT, but tritium is highly radioactive, and decays
away with a half-life of 12 years.
So you have to keep on replacing your bombs. So you could build the bomb
without the huge containers of liquid and you can make something was still
pretty big, but in principle could go in a giant bomber.
The first test of a lithium deuteride bomb was carried out, I think in 1954.
We feel of the report of this important test should give the failures as well as the successes.
The test name was called Castle Bravo.
The date was march, 1, 1954
This photograph was taken from an airplane at 50 miles.
The width of the fireball at this time, about three seconds after detonation, was four miles.
And it was really too successful.
The power of the bomb was three times bigger than had been calculated.
The tremendous field resulted in a serious fallout situation at Bikini and certain
other atolls downwind from ground zero.
The residents of the islands nearby had not been evacuated far enough and several people were exposed to radiation
in the most unfortunate manner. But the principal was demonstrated. Of course the
whole technology is horrific.
But it's interesting to see how lithium played a part. But to end on a much
happier note.
Lithium is a light metal. Hydrogen can be used to fuel cars, using fuel cells that
converts hydrogen to electricity.
So now there is a lot of research to see whether lithium hydride or a derivative
of lithium hydride can be used to store hydrogen in the tank of your car.
Which Sarin is one of them unfortunately terrorists can get hold of it I've got a
molecule of Sarin here
Not real Sarin. Not real Sarin, no, that would be illegal to make that, I've
made it out of straws and these coloured balls there.