Mercury and Relativity - Periodic Table of Videos

I've just read the paper which answers the question why is mercury a liquid motor is special because it's the only metal that's unarguably a liquid gallium you can melt when you warm it in your hands but mercury is the only metal that's liquid at room temperature it's even liquid if you stick it in snow so it's really no argument there's something special about it yes chemists and physicists have known for a long time it's a liquid because the forces between the atoms are weaker than they are say with gold or other elements but nobody has been able to do calculations to show why the melting point to mercury is minus 39 degrees centigrade but they have now and it turns out that the key to all of this is relativity in fact the article I've read has a special picture on the front of the journal cover which shows a picture of Einstein when he had had that looked like mine so it's really does connect relativity with mercury now the important aspect of relativity that's involved is the fact that relativity says that if you take an object and accelerate it to a very high speed close to the speed of light or a good fraction of it it becomes heavier how does this apply to natum well atom has a positively charged nucleus and a negatively charged electron going round and round so for a light a term like hydrogen which has just a single positive charge the electron goes round relatively slowly but as you get down the periodic table and get bigger and bigger atoms pretend this is mercury with a big nucleus the inner electrons have to go round at terrific speed or else they would tumble into the nucleus and in fact that speed becomes a significant fraction of the speed of light so the electrons become heavier and sink towards the nucleus so heavier atoms are actually smaller than you might expect because of these relativistic effects and you can do calculations to show that this has a genuine effect for example the go the color of the metal gold is due to relativistic effects of the electrons in the case of mercury what this paper has shown and it has quite a nice title evidence for low temperature melting of mercury owing to relativity it's quite a simple title and a very bold statement what they have shown is that you can explain the weak interactions between mercury atoms in terms of this relativistic effect now it's quite complicated in general the forces between atoms are determined by their size and by their electron distribution how the electrons are arranged and the smaller the atom and the more tightly the electrons are held so the weaker the forces now what this paper says which is very interesting is that if you take two mercury atoms isolated imagine in the gas phase the forces between them don't change very much with if you include relativistic effects in the calculations or not but it is only when you think of a whole group of mercury atoms as you would imagine in a small droplet or micro nano droplet that the relativistic effects become important and this work has taken a long time to do because you need a really big computer to be able to handle the calculations when you have a large group of atoms and you're doing the calculation about all those atoms at the same time in these calculations they have looked at the effect of putting a relativistic correction because you can do the calculation with an atom without taking a relativity in the count or with relativity in the count and so they've done this for two atoms and then they've done for lots and lots and lots which simulates the and in particular they can calculate the melting point that is when a solid metal turns into liquid and they've shown that without relativistic effects they calculate a melting point of 82 degrees centigrade which is only a little bit less than the melting point of sodium and higher than the melting point of cesium but with the relativistic effect the melting point drops to the close to the observed melting point of 39 degrees so they can actually calculate a number which is very close to the melting point of mercury what they are showing is that when you put in the relativistic effect and effectively contract the inner electrons of the motor atoms this has enough effect on the outer electrons of the atoms to stop the forces that would make it into a solid you can see even without the relativistic effects mercury wouldn't have a very strong interaction between the atoms it would melt at 82 degrees centigrade rather than the thousands of degrees that you find on some of the other elements but this is if you like the fine tuning the relativity that takes the melting point from a boring above room temperature to a really exciting below room temperature so the fact that mercury is a liquid is more proof that Einstein was right yes of course the next challenge is to do the same calculation with copernicium element 112 because it's in the same room as mercury and as you know that elements in the same group in the periodic table have similar properties so copernicium could have an even lower melting point so we look forward to the paper on the melting point of copán it's Ian and so this actually led people to suggest that there might actually be another planet that was perturbing the orbit of mercury that was even closer to the Sun so people came up with the idea that there was this planet called Vulcan even closer to the Sun that was actually causing it

Channel: Periodic Videos

Views: 297,422

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Keywords: chemistry, periodicvideos, periodic table, periodic table of videos, professor, martyn poliakoff, chemicals, elements, Mercury (Chemical Element), The Periodic Table Of Videos, relativity, einsten, electrons, atom

Id: NtnsHtYYKf0

Length: 7min 21sec (441 seconds)

Published: Tue Aug 20 2013