recently I got an email from a
journalist who's writing an article
about chemical bonding he asked me what
was the most surprising thing in my
lifetime about chemical bonding
fortunately it was an email so I had
time to think not sure what I would've
answered if I just been asked like that
but I decided that probably the most
surprising things involved the noble
gases when I was in high school about 14
years old it was discovered that xenon
could react with fluorine imagine it
there I was with chemistry teachers
telling me noble gases don't react with
anything and then suddenly is discovered
and not only discovered that xenon will
react with fluorine but it was found
that you could do it by just putting
them both in a glass bulb and leaving it
in the sunlight originally it was
discovered in Scotland where the Sun
isn't very bright it took a whole week
for the reaction to take place then they
did it in Chicago and it went which is
further south brighter Sun went in an
hour
suddenly there was this new surprising
fad and the amazing thing was that
really quite quickly
chemists understood it wasn't so
surprising and they could explain the
bonding then when I was a research
student doing my doctorate and a bit
afterwards we were working on very
reactive compounds of chromium and one
of my colleagues Robin one of my fellow
students demonstrated that chromium in
this compound could interact and react
with xenon this in really amazing and we
even made the model here it is you can
see it's beginning to be a bit faded but
it's got the chromium in the middle and
these five balls represent the five
carbon monoxide molecules that were
bonded to the
this is so-called chromium pentacarbonyl
it's got five Co molecules and the xenon
is bonded on here Robyn didn't actually
make enough of this material to put in a
bottle but he could observe its spectrum
and even its color it was over an orange
color the reason we made this model and
it's rather rusty now so it wouldn't
work was to demonstrate that you could
change the angle between this bond here
and these bonds down here these were
designed so that they would actually
slide down it's now stuck but they used
to slide up and down these slots what
was interesting is that my colleague
Jeremy Baudette who sadly died some
years ago worked out that when Zenon
came in here these bond angles changed
and this changed the color and so there
was a real surprise that Zenon could
interact with the metal and this is
perhaps for me what is the real surprise
about Zenon chemistry that we then
thought that Zenon has the same number
of electrons as iodide I - and nobody
surprised that iodide can react with a
metal so if you think about it the fact
that xenon can also interact with the
metal perhaps not quite such a strong
bond but could still interact is
reasonably obvious but what is
surprising is that no chem is to thought
about this until they've done the
experiments and I suppose it is one of
the great lessons about chemistry
because there's so many different atoms
and so many different compounds that
very often you find something which is
really surprising to you but then when
you think about it you can see that you
might have thought of it beforehand if
you'd known all the facts we're taught
that xenon is very stable all the
electron shells are filled everyone
content everything's neutral what
happens when fluid comes along that
breaks it apart that that makes things
change
well xenon cannot interact Stapley with
one fluorine atom because then you would
upset the arrangements of electrons
however if you have two fluorine atoms
it can as it were share one electron
with each and the three of them together
can still have quite a stable
interaction it's not terribly stable if
you heat the compound that it will
decompose back into xenon and fluorine
but it will interact reasonably stable
xenon and oxygen have a much more
unstable relationship and xenon trioxide
is a fantastically unstable compound
literally if you tickle it with a
feather it will explode xenon is pretty
inert compared to reactive elements like
fluorine or sodium or something like
that but its reactivity is not as
surprising as you might expect and
Krypton will also form compounds and
again with fluorine this very reactive
element you can just about get it to
react with chlorine but it's very
unstable but argon NIR and neon and
helium don't really for many compounds
that are stable enough to do any sort of
chemistry though there have been some
claims that argon can form complexes or
compounds at very low temperatures
inside the balloon is then accelerated
by the breaking balloon you can see it's
being accelerated hard down towards the
rest of the water and causing these
fantastic ripples these waves on the
surface and then this is continuing out
down so there's the water that we've
accelerated at the top from the balloon
bursting this way is now accelerating
out towards the bottom