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This is a balloon of Helium, and Helium is a very small gas.
we use in this case to find leaks in high pressure in high vacuum operators,
because it's very very small, finds the smallest, smallest holes.
But just like Hydrogen, it's also very very light.
And you know, in the past we used Hydrogen to fill balloons,
for transport, and now you see the Goodyear Blimp,
sporting occasions, filled with Helium.
So Helium is probably the most unreactive of the elements.
It has a mass of 4, so it weighs four times as much as a Hydrogen atom,
but Hydrogen is an H2 molecule, whereas Helium exists as isolated atoms,
so that the a Helium molecule weighs twice as much as Hydrogen.
See here, we have a Helium filled balloon, and it's extremely light,
so I'm not gonna let it go right now so I will lose it to the ceiling.
So I'm just gonna put on a piece of string. tie a lead around it again.
Helium can not be synthesized in nature because it is just an element.
It is found as a component of natural gas in some places,
particularly in the United States, because it is formed by the
radioactive decay of minerals underground,
and these form Helium, which is trapped with the natural gas.
So here we have a Helium balloon floating, because it's displacing
its volume of air, and it'll float quite nicely.
It's actually quite hard to contain, so the piece of string and the heavy
stand is there holding it down, because we don't really wanna lose it.
If we take a balloon of another light gas, and that's Hydrogen,
and we add a match to it or we set it on fire, it will burn really really quickly,
and really energetically, because it makes for lots and lots of water,
Hydrogen plus Oxygen.
We're gonna do the same experiment now, but we're gonna do it with
a Helium filled balloon, and see if that'll burn.
So here we have a technical match on a stick,
and we're gonna offer it out to our floating balloon of Helium.
Let's see what happens this time.
A little bit of a ***, but that's just *** of the gas escaping, it didn't burn.
Yep, it's unreactive, it's an inert gas.
The molecule is very light, so once it is in the atmosphere
it will eventually go out into outer space.
So that we are, in theory at least, likely to run out of Helium in eventual future.
If it is just released to the atmosphere.
So what I got here is a balloon of Helium, and it's really really light,
and it's displacing a lot of volume, so if I let go of it it's gonna fly like a balloon.
So what we're gonna do is I'm gonna hold it down here,
and Neil is gonna cool it for me using some liquid Nitrogen.
Now you can see Neil is using gloves, because it's very very cold.
Okay, so as he cools the balloon the gasses inside are slowing down,
and they take up much much less volume as we slow them down,
and now you can see it's displacing less volume,
so the balloon is quite happy to sit on the table.
If we stop pouring the liquid Nitrogen onto it now,
and watch what happens as the balloon starts to warm up again.
Because the gases are gaining more energy, and they are occupying more space,
and becoming more bouyant, so the Helium comes back to the ceiling,
where it really wants to be.
The Helium has a whole series of useful properties because it's a very light gas,
if you breathe in Helium, you then start speaking like Donald Duck,
in a very squeaky voice.
Helium. Fantastic element. Very light, very fun.
Because the speed of sound is much greater in Helium than it is in ordinary gases.
It is also very useful as a liquid. It only liquifies at very low temperature.
Its boiling point is -269 degrees centigrade. But if you cool things with liquid Helium,
you get very strange properties, for example, some materials lose their electrical resistance.
So liquid Helium is used for magnets when you need very powerful magnets,
and for example, they're used magnets from magnetic resonance imaging in hospitals.
If you use a vacuum pump to pump *** the Helium,
the boiling point will go even lower, and you can go to nearly two degrees absolute.
And so Helium is very important for all sorts of refrigiration.
Captions by www.SubPLY.com