there's one question which if you are
scanning chemist you can expect them to
answer no and that question is can you
find fluorine gas f2 free in nature and
they will say no it's far too reactive
as soon as fluorine sees anything it
will react explosively so how can
possibly you have f2 gas occurring
naturally it took hundreds of years and
efforts of chemists to isolate fluorine
in the first place
late last night I was reading an article
in a journal here which said first
fluorine gas found in nature and I was
amazed I really couldn't see even when I
read the title how it could possibly be
and it turns out to be quite an
interesting effect and something that
has been puzzling chemists for nearly
200 years
it concerns a mineral or chemical called
fluorite calcium fluoride caf2 this is
van quite widely in nature and is
normally a colorless crystal you can see
here this is a lump of it and there's
another piece here that's broken and it
looks almost like glass now about 200
years ago it was discovered that in one
particular mine in Germany and then
subsequently in other places there was a
form of fluorite which was quite dark
Lee colored so instead of being
colorless it had a dark purplish or
reddish color and when you ground this
apps or broke it up when you were mining
there was a terrible smell came out of
it and nobody knew why it's got quite an
interesting name it's not called
fluorite when it's this smelly sort it's
called an tazza night or sometimes it's
called fetid fluorite fetid ozone is a
rather nasty word meaning smelly but
with really sort of quite unpleasant
overtone dead bodies things like that so
what this new paper is about and there's
a press release that has come out from
the Universal there is a full paper
about it is that for the first time ever
people have studied the intact crystal
but without crushing it up because the
problem is though soon as you crush the
crystal and the smell gets out you've
lost it you can't analyze it in set by
sniffing it through your nose if you're
brave enough so what has happened is
that a lump of this material has been
put in an NMR machine nuclear magnetic
resonance which can detect various
chemical forms fluorine the element F
and from the NMR signal they worked out
that in this smelly fetid fluorite there
are tiny bubbles of fluorine f2 so you
can argue how can you get a gas in the
middle of a crystal and the answer is
that this material has trace impurities
of radioactive elements like uranium or
thorium and when these decay and give
off alpha particles or beta particles
those interact with the fluorine and
turn f- into fluorine gas and this gas
accumulates as tiny bubbles in the solid
f- is the fluoride ion in calcium
fluoride you have CA 2 plus and 2f minus
ions so what happens is you get f2 and
the calcium atom now of course the
calcium atom is just sitting there and a
number of calcium atoms will clump
together and in fact this strange color
this dark color is in fact the
absorption due to the clusters of
calcium atoms and that was discovered
some time ago but the question was what
form was the fluorine in and now they're
shown it's f2 so although fluorine is
very reactive the gas is very reactive
it doesn't react with calcium fluoride
because that's already reacted with
fluorine so it's because it's made in
the middle of the crystal it can exist
it's as if something has grown inside
the bottle and therefore it cannot get
out professor why doesn't it re react
with the calcium that is split apart
from well presumably what happens is
that they're tiny cracks or whatever in
the crystal and the gas diffuses away
sufficiently far that when it's trapped
there it's separated from the cluster of
calcium
atoms and there's no reason why it
should go back like a bubble in the
spirit level perhaps or anything that's
included and cherry in the cake like you
can see up there and when you grind up
the rock out it comes now the
experimenters tried smelling various
different gases hydrogen fluoride
various fluorides of sulphur and also
hydrofluoric acid HF and none of them
quite smelt the same as the f2 gas I'm
slightly surprised because f2 reacts
with water very quickly to form hydrogen
fluoride and since the inside of one's
nose is wet I would have thought it
would have reacted immediately but
perhaps because smell is a very
complicated sense it doesn't rip behave
in quite the same way as HF and gives
you a different sensation but the
important thing is that this experiment
shows us that our most cherished beliefs
that f2 is so reactive that it could
never occur in nature is wrong and as
you may have heard me saying on other
videos it's really important for
chemistry that we keep on having our
ideas challenged that we've shown that
things that we believe are wrong because
that will give us all sorts of new ideas
that could be very useful
right in there it is
Oh
you