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  • Now, of course, the most famous thing about helium...

  • Or at least the thing that most people know, is if you breathe in helium, it makes your voice change.

  • Makes it go squeaky.

  • I've never tried this...

  • So, I decided that it'd be rather fun to try this time with Neil and Brady helping me.

  • [Brady ] Are you nervous then?

  • Erm. No, I'm not nervous yet.

  • Well, I am nervous, I've just read on Wikipedia that somebody died after breathing helium.

  • But I hope it won't happen now.

  • Make a good video if it does. *takes a breath of helium from balloon*

  • *higher pitched* Hello, I'm now talking with helium in my voice.

  • And it quickly goes away.

  • And the first time I did it, I didn't breathe deeply enough so my voice didn't change very much.

  • But the second time, it did change really quite significantly.

  • *takes second breath of helium from balloon*

  • *an even higher pitch* There are a hundred and fifteen more videos to watch.

  • In fact, there are a hundred and seventeen more videos to watch.

  • Was that different?

  • When you're doing it, it just feels as if you're talking normally, but somehow your voice comes out differently.

  • I suppose it's like when you have a very bad cold or something like that that, your voice changes as well.

  • I don't think that this is a good experiment for you to try yourselves.

  • I don't think it's dangerous if you do it just once.

  • But if you keep on breathing helium, it can be really quite dangerous.

  • And in fact, I read recently about somebody who died after breathing too much.

  • But if you breathe helium under controlled conditions, it's quite safe.

  • And in fact, it's used for deep-sea divers.

  • One of the problems if you're diving very deep under the sea...

  • Is that, you have to breathe air that's under pressure; otherwise you can't open and shut your lungs.

  • Under pressure, the nitrogen in the air dissolves in your blood.

  • Now, this doesn't matter when you're down at the bottom.

  • But as you come up, if you surface too quickly, the nitrogen can come out as bubbles in your blood.

  • And cause a very painful condition...

  • Which for some reason, the divers called the "bends".

  • And it's been found that if you replace the nitrogen in the divers breathing air, or at least most of the nitrogen with helium...

  • Then they don't suffer from "bends".

  • [AP Archive voice over] "Below 150 feet, the pressure on the body rises dramatically and divers must operate on a mixture of helium and oxygen."

  • But of course their voices go squeaky...

  • So the people on the other end of the telephone, talking to the divers, need to have some sort of electronic filter...

  • So that the divers' voices are transposed and they can still understand what they're saying.

  • The reason why your voice changes is probably due to a number of factors.

  • One of the factors is that the speed of sound is much greater in helium than it is in air.

  • The reason for this, is that the speed of sound is related to the mass of the molecules in the gas that the sound is going through.

  • And the helium molecule is much lighter than nitrogen or oxygen, which you find in air.

  • Of course if you breathed hydrogen, it would be even faster the speed of sound, but you then blow yourself up.

  • So this is not something that anybody should try.

  • The other point, is that inside the Human head,

  • in fact, the head of all animals, there are complicated resonances caused by the different spaces.

  • And that's why your voice changes when you have a cold,

  • because some of the tubes are blocked.

  • So, I had the idea...

  • that perhaps, if you put an iPhone playing music in helium, that the sound might change.

  • Though there isn't much to resonate in an iPhone.

  • *music from iPhone*

  • But Neil and Brady were quite keen to try.

  • And our first experiments with a small plastic bag were a bit of a failure.

  • So then Neil got a really big plastic bag and filled it with helium.

  • And when you put it over the iPhone.

  • Most surprisingly,

  • the notes didn't change, but the sound was attenuated much more.

  • *music continues*

  • So it sounded much quieter.

  • *music continues*

  • I'm not sure why this is, but it was quite a striking effect.

  • And Neil put the bag on and off.

  • *music continues*

  • And you could hear the music getting louder when the bag was not there and going quieter again when he put it back.

  • *music continues*

  • And we did a control experiment with a bag of air, and it wasn't the bag it definitely was the helium.

  • But the thing I liked best was that Neil then let go of the bag, and it went up to the ceiling and stayed there.

  • Even though the bottom of the bag was completely open.

  • So once the helium is trapped in an upturned plastic bag, it will sit there for quite a long time.

  • *music continues*

  • Because helium is an inert gas...

  • Because it has two electrons that are paired...

  • It doesn't form conventional chemical compounds in the way that say hydrogen does or sodium.

  • But there's a very recent paper published just a few months ago,

  • in this journal here, where you can see it says "Noble gas compounds: when helium met sodium".

  • And the people here have done a really extraordinary experiment,

  • where they mixed sodium metal in helium gas in a diamond anvil cell.

  • We have a video that explains how these work.

  • But in these cells, you can get really high pressures.

  • In their case, they went up to a pressure of nearly three million atmospheres.

  • Three million times higher than atmospheric pressure.

  • And when they did this they found, remarkably, that sodium metal...

  • forms a compound with helium.

  • Where there is helium which is still chemically neutral: not helium plus or helium minus.

  • And sodium and in the lattice between them, there are two electrons.

  • Which are sitting there. Now normally in sodium metal,

  • because it's a metal, the electrons are,

  • if you like smeared out, de-localized through the structure,

  • that's what gives it its metallic properties.

  • But in this salt: Na2He.

  • Two sodium atoms for each helium atom, the electrons are localized and they predicted, but they weren't able to observe...

  • That actually under these high pressures the sodium and helium mixture should become transparent.

  • So it's really quite exciting.

  • So if your teachers tell you that helium doesn't form compounds.

  • They're both right and wrong.

  • They're right, because it doesn't form compounds under normal conditions, but they're wrong because at three million atmospheres, Yes, you can get some.

  • The reason why there is helium in the Sun.

  • Is partly because the nuclear reactions that take place in the Sun...

  • are responsible for creating helium.

  • Hydrogen atoms, under these enormously high pressures and temperature,

  • the hydrogen atoms can fuse together, by a process called fusion, to generate helium.

  • Now and the normal circumstances, it's not possible to do this on Earth.

  • But if you take a nuclear bomb,

  • you can use an atom bomb to trigger the fusion of, usually deuterium or tritium...

  • these are isotopes of hydrogen and they can be made to fuse to create helium.

  • [Archive voice over] "On this rather unimpressive barge, floating in the Bikini Lagoon,

  • rests the device which carried the hopes for a large step forward in the weapons development program."

  • *muffled sound of a nuclear explosion*

  • "The distance of the camera aircraft is 50 miles. The frame size of the picture is 14 by 18 miles,

  • the film is running at normal speed."

  • There is also hope that you can do controlled fusion in reactors called Tokamaks.

  • Where eventually, it may be possible to use the fusion of hydrogen atoms to make helium...

  • as a way of generating very clean electricity.

  • However, experiments have been going on for most of my lifetime,

  • and although the results are promising, they're nowhere near being commercial production of electricity.

  • The most common isotope of helium is helium-4: with two protons and two neutrons.

  • There is a very rare isotope, helium-3, which has two protons and one neutron.

  • And the properties of liquid helium-3 are significantly different from the properties of liquid helium-4.

  • Because at the very low temperatures of these liquids, the quantum effects become very important.

  • In fact, I've read, and I don't know if it's true, that liquid helium-3 and liquid helium-4

  • are immiscible, they don't mix together, which is really quite weird?

  • Helium-3 can also behave as are superfluid, which means that it can creep upwards out of its container.

  • Whereas, normally, if we put a liquid, say tea into my cup, it stays there, but imagine if it crept up the sides and went out.

  • So helium is a really very exciting element.

  • [Brady] Alright, let me start the music...

Now, of course, the most famous thing about helium...

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Helium (some extra stuff) - Periodic Table of Videos

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    林宜悉 posted on 2020/03/27
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