Notes

Uranium belongs to the actinide series in the periodic table

that is,to radioactive elements

and its atomic number is 238.

Uranium is 40 times more abundant in Earth's crust than silver.

It is so abundant because it forms

upon rapid neutron capture inside spinning supernovas.

That is why Uranium was discovered quite early

in Germany

in 18th century.

Its discoverer, Martin Heinrich Klaproth

named it after a newly discovered planet of the solar system

after Uranus.

In nature, uranium is often found in such minerals as uraninite and autunite.

This metal often has several oxidation states in those minerals

Thanks to the beautiful yellow colour of such minerals

glass-blowers added them to glass

As a result

minerals would give such a glass

a beautiful greenish colour.

It's a pity that back then

craftsmen didn't know about the toxicity of uranium compounds

Nevertheless, pure metallic uranium can be obtained from uranium ore

via reduction by calcium.

And it looks very ordinary.

Since mostly uranium naturally occurs

in the form of uranium-238 isotope

with a half-life of about 4.5 billion years

depleted uranium is most frequently used for chemical research

in order to reduce scientists' exposure to its radiation.

Pure uranium obtained from its ore looks quite dark

as its surface oxidises pretty fast

because of the high chemical activeness of this metal.

That is why it is often stored in argon

and also all experiments with uranium are conducted in argon atmosphere.

Usually, to conduct experiments a piece of uranium-238

is ripped to such small shreds on a lathe in laboratory.

It is noteworthy that these shreds in the test-tube

already emit beta and gamma radiation

Gamma emission alone is 50 times the normal level.

This emission is caused by the decay products of uranium

which breaks down even further

to beta and gamma particles.

The walls of the test-tube confine the alpha-rays.

Because of its high chemical activeness

uranium shreds burn well in the air

For the first time on YouTube

you can observe how uranium burns

and turns into its oxides.

However

to conduct experiments uranium is not just burned.

Uranium shreds are mixed with iodine crystals

and the chemicals are left to sit for a few days

sometimes with a solvent

in order for them to react.

The reaction produces uranium triiodide

of such violet colour.

The reaction can also produce uranium tetraiodide

depending on the proportions of reagents.

These metal compounds, with +3 or +4 oxidation states

are most frequently used as raw materials to create uranium complexes

and are also used as catalysts

because with such an oxidation state uranium is the most chemically reactive

because of having a lot of electrons in the f-orbitals.

It is noteworthy how quickly the colour of uranium compounds change

depending on the oxidation state.

For instance, it can be seen

when comparing uranium triiodide and uranium tetraiodide.

It is also worth noting

when tetrachloride is used instead of uranium tetraiodide

the colour will also change drastically

from orange to green.

By the way,

uranium tetrachloride used to be used

in early electromagnetic isotope separation uranium enrichment

But soon this method proved to be inefficient

and was substituted by other methods.

Nevertheless, uranium compounds with +4 oxidation state

are quite stable.

That is why they are used most frequently.

For instance, enriched uranium dioxide is used

as nuclear fuel for atomic reactors.

However,

the oxidation state of uranium can be increased

to +6 oxidation state.

For instance, dry uranyl nitrate is a beige powder.

In this form it is most frequently used for experiments.

When exposed to air

this compound absorbs water very well

and it turns into beautiful hexahydrate crystals

which glows in ultraviolet light very well.

Uranyl nitrate is also formed when pieces of uranium react with nitric acid.

Besides, at this particular moment

the shiny surface of the element can be seen very well.

In fact, many compounds of 6-valent uranium have fluorescent properties in ultraviolet light.

That is the very reason why they are added to so-called uranium glass

which beautifully glitters in the sun with bright green colour.

Whereas, in the dark, when an ultraviolet flash-light is pointed at it

it looks even more stunning.

Because of its fluorescent properties, uranium is most frequently depicted as glowing with green

in most cartoons and films.

Although in reality uranium fuel and uranium itself are usually of dark colours

and don't attract much attention.

Besides, it's worth remembering that many uranium compounds are very toxic

and, needless to say, are also very radioactive.

There are also uranium compounds with +5 oxidation state

However, only in 2006

stable uranium compounds with +5 oxidation state were obtained

that didn't break down at room temperatures.

It was achieved as a result of stabilisation of uranyl ion

with the help of organic coordination ligands.

And, if you think that scientists were doing useless things

I hasten to question that statement.

Nowadays, because of the large amount of processed nuclear fuel

there is always a risk of water and soil contamination

with well-soluble 6-valent uranium compounds.

However, if they are converted to +4-valent uranium compounds

they do not dissolve in water.

The risk of water contamination decreases by a few times

because 4-valent uranium compounds will just sink to the bottom

and can later be easily collected.

Also, 5-valent uranium is often stabilised by iron ions

for instance, in such an iron ore as magnetite.

That is why now scientists are seeking to use it for a more efficient nuclear fuel recycling.

And now, let us recall to the title of this video

and answer the question

Why uranium is so dangerous?

It's so because this is the very metal that the Little Boy bomb, dropped on Hiroshima in 1945, was made of.

This bomb was designed using a gun method.

Two parts of enriched uranium in sub-critical state

were shot in each other.

After being in contact, the mass of uranium would reach a critical point

and this would trigger a chain reaction

when uranium cores would start dividing

under the influence of an enormous amount of neutrons

which reflected off the tamper, made from tungsten carbide.

As a result, the nuclear explosion killed about 2,000 people

becoming the first use of atomic weapons in history.

Besides, in a nuclear reactor uranium-238 can be turned into plutonium-239

by irradiation with slow neutrons.

It is known that plutonium-239 is fitting for making implosion-type atomic bombs

because its critical mass is smaller.

As if that was not enough

uranium is also a very toxic metal

That is why, because of these dangerous properties, it can be called the most dangerous metal.

It is also worthy of note that naturally occurring uranium

mostly consists of isotope uranium-238

which cannot divide spontaneously

and is not suitable to be used for making nuclear weapons.

Only less than one percent of uranium

or more precise, uranium-235

can run a self-sustaining nuclear chain reaction

and can be used to make atomic bombs.

To make those bad things

the concentration of isotope 235 is increased...

to 85%

whereas only 3% of uranium-235 is enough to make nuclear fuel for power stations.

Usually enrichment is done by centrifugation of gaseous uranium hexafluoride

in special machines.

During this process a lot of needless uranium-238 is released

and concentrated.

That is how depleted uranium is obtained.

Its radioactivity is much smaller than that of enriched fuel.

As a result of the cold war, there has been produced too much depleted uranium

that people don't know what to do with it.

Thanks to its high density

depleted uranium is used as aircraft loads for balance

as tank armour

and even as missile cores.

However, because of being highly active

uranium armour can ignite

and that is why it can be risky to use.

It's also noteworthy

that because of the very long half-life of uranium

it is still a source of warmth of Earth.

To make a conclusion, we can say

that uranium is the most dangerous metal on Earth

because it's very toxic

and people have made one of the most destructive weapons from it.

One step in the wrong direction can lead to disastrous consequences.

Chernobyl nuclear disaster is a testimony to that.

Humans have yet to find an efficient way of recycling uranium

with as little impact on nature as possible

and also to decrease the risk of nuclear disasters

and environmental contamination.