Argon - Periodic Table of Videos

Neal and I have come up with a couple of ways of showing you a transparent gas in a rather more interesting way first of all like all gases argon can be liquefied it has a melting point and a boiling point both of them slightly higher than the temperature of liquid nitrogen [Applause] they're quite unusual because there's barely 5 degrees centigrade between the melting points and the boiling point most liquids have quite a long liquid range you can heat them quite a bit after they're melted before they boil argon has this tiny range but Neil with his magic experimental fingers has managed to liquefy really quite simply in the same way that we make liquid oxygen by passing argon gas through a coil that is cooled with liquid nitrogen the argon passes through the coil faster than it can freeze and you can collect the liquid in the thermos flask a Dewar vessel as you know we have a special dual vessel that's not silvered so you can see what's inside very easily and you can see argon boils as a colorless liquid looks rather like nitrogen but if you measure the temperature you'd find it was boiling at a slightly higher temperature I get quite excited saying liquid argon partly because I've never actually seen it before in a Dewar but also because we used to do research using liquid argon as a solvent [Music] and in fact I got the cell we used to use here the cells made out of copper and it's cooled with liquid nitrogen that goes through one of these pipes and out of the other there's a little chamber inside with windows that are transparent to infrared light the windows themselves are quite exciting let me show you if I shine my phone through it you can see that the windows are red and they're red because they're made of a compound of tylium and bromine and iodine it has the rather and romantic name of Krsna liam is very poisonous you mustn't touch it and you'd spoil the experiment anyway if you touched it the reason we were using liquid argon as a solvent is because we were doing infrared spectroscopy and looking at the spectrum of dissolved molecules infrared light is absorbed by the vibration of atoms but argon has only one atom in the molecule so it can't vibrate so it is completely transparent infrared light unlike nearly every other solvent water for example absorbs infrared light very strongly so you can have a very dilute solution in liquid argon and you can get a wonderful spectrum because it doesn't absorb and because it's cold you can see the behavior molecules in solution at much lower temperature than in most other solvents argon is used in the lab as just an inert gas when you are handling compounds that react with oxygen if you are looking at not very valuable compounds you very often will use nitrogen because nitrogen isn't much cheaper than argon but because the atoms of argon is much heavier than the molecule of nitrogen it's much more efficient in chasing air out of the remote corners of your apparatus so for really air sensitive compounds argon is better in the 18th century there was some indication when people were analyzing air that there was an extra one cent that was not nitrogen but there had no means of identifying it and it was only in the 1890s that Lord Rayleigh and Ramsey first managed to identify argon particularly by putting electric current through the gas and observing the light that is emitted Neil has got out one of our noble gas stars this time filled with argon and when you put a current through it you can see it gives out a very nice blue color quite different from the orange of helium or the red of neon and the light consists of a number of lines different colors which is essentially what was observed at the end of the 19th century when argon was identified the name argon apparently comes from the Greek word meaning Idol because it doesn't react with other things but even that's not correct now because there are a whole series of experiments that have been done looking at the reaction of argon at low temperature and if you condense argon and hydrogen fluoride HF at 20 degrees absolute and shine light on them to dissociate the HF you can make a molecule which is hydrogen argon fluorine it's only stable at very low temperature but there was huge excitement when it was discovered because it was the first compound of argon well it wasn't quite the first compound because early on in my career my fellow student Robin Perutz was studying at the reactions of a chromium compound in solid argon at 20 degrees absolute the molecules were isolated a bit like the cherries in a cake and when you shine light on the chromium compounds they dissociated and the chromium atom could react or interact with argon now it wasn't a very strong bond but it was enough to change the color of the compound and it made a beautiful purple color which I photographed and have used as a slide ever since the final and I have to admit perhaps slightly boring application of argon is in double glazing to keep our houses warm because argon has a heavy atom the atoms don't move very fast in the gas phase and therefore they're bad conducting Heat so if you have double glazing that's two sheets of glass in your window if you put argon between the glass it is much more effective and insulating the inside of the house keeping cold out then if you use air because air has a much higher conductivity of heat so if you look out of the window you may find that you're looking through argon gas [Music]

Channel: Periodic Videos

Views: 265,513

Keywords: periodic, videos, chemistry

Id: N0Gw6-xMLlo

Length: 8min 6sec (486 seconds)

Published: Mon Jul 30 2018