[Disclaimer]
Hello everyone.
Today, I'll tell you about the most toxic metal on Earth,
about Thallium.
In the period table of chemical elements,
Thallium lies on the bottom of group 13,
and have the atomic number, 81.
Let us start with a little bit of history
Thallium was first discovered
in 1861, by English scientist William Crookes,
and also simultaneously by French chemist Claude-Auguste Lamy.
It was discovered thanks to the green flames
that compounds of this metal would give.
Thallium was discovered
when scientists studied rocks containing Lead
Nowadays, it's mostly extracted from sulfuric heavy metals, such as Crookesite and (Hutchinsonite?).
In our laboratory,
I got quite-old pieces of thallium for my experiment,
they were produced back in 1970s.
Since then, they have been strongly oxidized
and covered in a dark thallium oxide.
Usually to protect thallium from getting oxidized,
it is store it in glycerol.
Don't worry!
We have taken out the necessary precautionary measures
Don't try this at home
To see the shiny surface of metallic thallium,
I submerged my piece of thallium
in concentrated nitric acid
where it slowly began to dissolve
forming nitrites (Correction: nitrates) of this metal.
Thallium's oxides can be washed away
The metal looks shiny with bluish shades
Without its oxide, this metal can easily be confused with tin
or other safe metals
That is why thallium is quite treacherous
It can easily be melted down
because its melting point is just 304C.
Molten thallium oxidizes very quickly
when exposed to air,
coating in dark thallium oxide layer.
This sets it apart from other metal belonging to group 13.
For instance, chemical activity of metals,
starting from aluminium and finishing with indium, steadily decreases.
Indium doesn't even oxidize when exposed to air
and remains shiny.
Thallium, however, is more active
and not only has the +3 oxidation state,
as other metals place here (in group 13) in the period table do,
it also has +1 oxidation state,
which is quite unusual.
Thallium used to be considered an alkali metal for some time after it was discovered.
If an oxidized droplet of thallium is submerged in nitric acid,
the oxide layer will immediately dissolve.
After that, the metal's shiny surface can be seen.
Thalliums hardness is similar to that of lead:
It's also quite soft,
and can easily be twisted.
We also used to have thallium(III) nitrate we could use
for a few experiments in our laboratory
By the way, thallium compounds are the most toxic among all the metals
because, toxic arsenic, for instance, belongs to metalloids class.
But we will speak about toxicity a bit later
Having put out all the fears,
I switched the fume hood to maximum suction setting.
I continued running my experiments with this element.
Thallium(III) nitrate doesn't dissolve in water that well
and looks like white crystals
Thallium compounds, for instance, thallium(I) sulfate,
can be widely used as rat poison until 1972.
But later on the practice was abandoned,
and it became clear
that thallium(I) sulfate was toxic to people too.
If you add potassium iodide to thallium(III) nitrate solution
it will form beautiful yellow thallium(I) iodide sediment.
In spite of being toxic,
this chemical has a few applications.
First of all,
it's used in metal halide lamps,
which beautifully glow green when heated up
because of Thallium ions.
The second application is mixing thallium(I) iodide with thallium(I) bromide to make optical crystals
that infrared light can perfectly pass or be refracted through.
Another unusual property of thallium
is that its chlorides are insoluble in water
like silver chloride.
Such thallium compounds are also used in optics and laser appliances.
It's quite surprising that such a toxic metal, thallium,
has so many applications, isn't it?
Before the technological era,
this metal has been mostly used as a poison,
because all thallium compounds are tasteless.
The lethal dose of thallium(I) sulfate when taken orally
is only 1 gram.
After ingestion,
thallium combines with sulfide groups of amino acids.
This ruptures the proteins,
which can become a chain reaction
leading to the death of the entire cell.
Especially, nerve cells suffer from thallium poisoning.
The action of the poison is disguised as a flu or bronchopneumonia,
which (makes thallium) especially dangerous
Thallium also used to be called the poison of poisoners.
And YOU, who are watching this video,
do not abuse the knowledge you have received, okay?
I'm saying this just to be on the safe side.
But, modern day scientists, don't beat around the bush
in our part in what used to be poison only, there's good use!
For instance,
not a long time ago,
it was discovered that thallium, colbalt, calcium, and barium oxides
Can be used to make high temperature, highly conductive ceramic,
which becomes superconductive at -148C.
Nowadays, thallium is even used in medicine
Isotope thallium-201 is used in scintigraphy,
i.e. getting 2-dimensional images of organs.
To sum up, we can say
that the world is changing
And what used to be used as a poison
can now be used to treat disease,
and also to light up the streets.
Now you know a little bit more about one of the other metals
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