Name: Helium - Periodic Table of Videos
Uploaded: 2020-03-27T18:11:21.000Z
Duration: 11 min 11 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

[HIGH PITCHED]: There are 115 more videos to watch.

In fact there are 117 more videos to watch.

Helium is the second element on the periodic table.

But it's very rare here on the planet Earth.

In fact, It's the only element in the periodic table

that it was first discovered outside our planet.

came when people were looking at the spectrum of the Sun,

in 1868, the year before Mendeleev proposed the periodic table,

and they noticed a single very bright yellow line.

The yellow line is due to the electrons in the helium atom being excited.

This is a glass star filled with helium gas.

you can excite the electrons in the helium and it emits light.

the very yellow line that was detected in the Sun's spectrum.

To begin with they thought it was sodium.

But then they realized it must be a new element,

it was given the name helium from the Greek word helios.

Which is, I believe what the Sun is called in Greek,

with people were examining a uranium mineral,

of natural gas coming out of gas fields in the United States.

The reason why you find helium associated with uranium,

And the naked nucleus of helium is what are called alpha particles

that are emitted during radioactive decay.

So if a radioactive atom decays and emits an alpha particle

the alpha particle quickly picks up a couple of electrons

And over millions of years this can accumulate in gas field.

all of the helium in the world has come from radioactive decay,

that has come from people letting off hydrogen bombs.

[ANNOUNCER]: The width of the fireball at this time, about three seconds after detonation, was four miles.

[PROFESSOR]: Helium in the natural gas was discovered

fairly shortly before the first World War.

And so it was quickly realized that this gas could be useful

for observation balloons on the Western Front on the battlefields.

[ANNOUNCER]: The enemy's troop movements and defense schemes are under constant observation

by French and British Airmen as well as by observation balloons.

[PROFESSOR]: Because unlike hydrogen it doesn't burn,

So helium started to be produced as a strategic material.

[ANNOUNCER]: Non-explosive gas for dirigibles. America has a virtual monopoly of it, helium.

[PROFESSOR]: So there's a long history in the United States

of legislation for conserving helium for strategic defense purposes.

[ANNOUNCER]: The subject has of course attracted great attention all over the world

because of the terrible Hindenburg disaster.

The American president's cabinet committee is convinced

that helium should now be made available to Germany

[PROFESSOR]: So a helium nucleus, or helium atom,

weighs four times as much as a hydrogen atom

But because hydrogen exists as an H2 molecule,

helium atom, which is the same as its molecule,

weighs twice as much as a hydrogen molecule.

has devised quite a nice little demonstration,

can actually pull the helium balloon downwards,

because there's a lot more lift in a hydrogen balloon

than in the helium one, because the hydrogen is lighter.

The most important property for helium, nowadays,

it forms the coldest liquid that one can obtain.

Liquid helium boils at minus 269 degrees centigrade.

So you can use liquid helium to cool materials down.

And particularly, you can cool certain alloys of metals

which lose all their electrical resistance at low temperature,

which can be used to build really powerful magnets.

Particularly for our university, for magnetic resonance imaging,

for looking inside people's bodies to see that all is well,

And so our university has a plant for liquefying helium.

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Helium - Periodic Table of Videos

realize

spectrum

squeeze

molecule