9 ms·

What mercury being liquid at room temperature has to do with relativity

140 points by halostatue 13y ago

Vivtek 13y ago
Could somebody please make that lower-case "mercury"?
- twiceaday 13y ago
  Every time there is an edit, no matter how small, the article shows up once per edit in my RSS feed. I think edits should be kept to a minimum or not published multiple times.
  - jlgreco 13y ago
    I de-dup based on both title and URL such that changing one won't cause me to see it again unless the other is changed at the same time; it seems to help.
    - alien_acorn 13y ago
      What reader are you using that offers de-duping?
  - alxndr 13y ago
    Interesting; does the id in the URL change?
  - baddox 13y ago
    A really cool idea would be a site where people can submit anything they want with any title they want, and users' votes will determine how the stories get sorted. That way, the community could easily express and realize their preference for titles by upvoting the ones they prefer.
    - bobbles 13y ago
      The problem with a system with no moderation is that the abusers of the system have more time and incentive to abuse than the community does to moderate.
  - deleted 13y ago
    [deleted]
sgtnasty 13y ago
I wish I could understand this.
- Nursie 13y ago
  What I'm getting from this is that - > under relativity fast things are heavier > electrons are fast, they actually have about a 23% weight boost > heavier electrons 'orbit' closer to the nucleus > the atomic size is then smaller than anticipated > this has a bunch of interesting effects on melting points, reactivity, colour/reflectivity etc, (especially of transition metals?) > this stuff has not always been well understood. It's been a long time since I studied chemistry, so I may be reading it wrong. It's pretty cool though :)
  - VladRussian2 13y ago
    inter-disciplinary science of such effects http://en.wikipedia.org/wiki/Relativistic_quantum_chemistry http://en.wikipedia.org/wiki/Relativistic_quantum_chemistry
deleted 13y ago
[deleted]
mjfl 13y ago
There is another interesting Q/A on physics.stackexchange about why gold is... gold. http://physics.stackexchange.com/questions/72368/why-are-most-metals-gray-silver http://physics.stackexchange.com/questions/72368/why-are-mos...
- minikites 13y ago
  And here's an interesting story on why gold was destined to be used as currency: http://www.npr.org/blogs/money/2011/02/15/131430755/a-chemist-explains-why-gold-beat-out-lithium-osmium-einsteinium http://www.npr.org/blogs/money/2011/02/15/131430755/a-chemis...
  - jameshart 13y ago
    Interesting that it misses what I always thought was the most important property of gold in this regard which is that it is (for a pre-technological society at least) completely unadulterable. It's the densest material you can readily obtain, without the ability to smelt platinum (whose melting point issues were mentioned in the article as a disqualifier for functioning as money). That means that I can't make a coin that matches both the size and the weight of a real gold coin out of anything other than gold. If you'd picked iron as the precious metal, I could fake an iron coin by mixing tin and lead together so the alloy's density matches iron's. But to make a fake gold coin without using gold, I need to mix something lighter than it with something heavier - and my options looking for something heavier are either in the platinum group, or are heavy radioisotopes like Uranium. All of which are probably sufficiently rare in a pre-technological society that they're worth more than their weight in gold anyway, so not much use as raw materials in a forgery. Density is destiny...?
dnautics 13y ago
Ok. So what is interesting here, is that chemists have long suspected this (to the point that this explanation was dogma to me as a grad student) but new paper gives it a fairly rigorously demonstrations from first principles in a less-handwavey fashion.
spuz 13y ago
Interestingly the actual melting point of Mercury (according to Wikipedia) is 234.3210K which is still a way off the 250K calculated by this study. I wonder how realistic is it to exactly calculate melting points of metals and other materials from first-principles?
- shmageggy 13y ago
  Well, it's an order of magnitude closer than the 355K that was predicted without accounting for relativity, and I think the point was that a melting point of 355K (82C) means it would be solid at room temperature, while 250K (-23C) means it is liquid at room temperature, so they can conclude it's the relativistic effect that's responsible for its weirdness. tl;dr: close enough.
- Florin_Andrei 13y ago
  It's a miracle they did it anyway. I still remember calculating the hydrogen atom back in college. It's a trivial case compared to mercury, yet it takes a surprising amount of scribbling. I assume they did all sorts of approximate models for mercury. An analytic, rigorous solution must be impossible.
andrewflnr 13y ago
If it's just about the electrons being pulled closer to the nucleus, why doesn't the effect apply nearly as much to it's neighbors on the periodic table?
- wiredfool 13y ago
  Because it's the one with full d orbitals as the outer electrons.
  - VLM 13y ago
    To extend on wiredfools remarks, the effect of non-full means lots of electron sharing going on. But if they're full, the (smaller) effects of relativity are the only effects so they're dominant. The neighbors are non-full so the sharing they do is way more important level than relativity level effects.
evanb 13y ago
The explanation, as described in the article, is lacking, since it does not really explain why no other elements are liquid. The suggestion is that it is that the 6s orbital is full. Why don't other large-Z elements with filled p- or d- or f- orbitals also become liquids?
- VLM 13y ago
  TLDR is they do. The medium form answer is look at the periodic table. There's block of s (which don't count because other than H/He they are buried deep in the atom) and a block of d where the full ones do have ridiculous low melting points compared to neighbors (like Zinc, Cadmium, Mercury...) and a block of p shell where the full p shells are the well known noble gases which are liquid at really low temps and the block of f weirdos who don't matter. As for the f weirdos not mattering look at the electron configuration for something like Tb. Yes very nice that it has a peculiar collection of 4 level f shaped orbital electrons but I guess the more influential effect is the 5 level s and 5 level p and more importantly the 6 level s way out there in front of the mere 4 level f. Its kind of like D+D or pathfinder multiclass, oh, you have 2 levels of bard multiclassed into your level 10 sorcerer, well whatever, that bard isn't going to matter very much compared to the sorcerer level powers. So back to your question, the filled p make great gasses at room temp not mere liquids you are totally correct here, the filled d have really low melting points for metals like Hg being a liquid as discussed, and the filled f are weirdos who fool around with electron configurations at mere level 4 when the real chemical action is at level 6 so they don't matter (sorta) For a more correct, longer form answer someone else will have to step in.
  - davvolun 13y ago
    Favorite analogy ever. Don't really know why the 4 level f shaped orbital electrons are a level 2 multiclassed bard and the two 5 level s/p and 6 level s are like a level 10 sorcerer, but that may be because I understand about 5 of the words at the beginning of this sentence. It's been a really long time since chemistry.
    - jjoonathan 13y ago
ttflee 13y ago
It seems quite bizarre that the introductory chemistry about elements is taught without the prerequisite knowledge of Schrödinger equation and special relativity in college.
akincisor 13y ago
Gallium melts not much higher than room temperature... Is that explained by orbitals as well?
cantrevealname 13y ago
> the electron approaches about 58% of the speed of light, and its mass increases to 1.23 times its rest mass Does this mean that as mercury is cooled to absolute zero, the electron will slow down and mercury will become lighter?
- raverbashing 13y ago
  No. You can't have an electron filling lower energy levels if they're already occupied. Also, I'm guessing what they mean by "electron speed" is actually electron energy.

140 points by halostatue 13y ago

Vivtek 13y ago

Could somebody please make that lower-case "mercury"?

twiceaday 13y ago
Every time there is an edit, no matter how small, the article shows up once per edit in my RSS feed. I think edits should be kept to a minimum or not published multiple times.
- jlgreco 13y ago
  I de-dup based on both title and URL such that changing one won't cause me to see it again unless the other is changed at the same time; it seems to help.
  - alien_acorn 13y ago
    What reader are you using that offers de-duping?
- alxndr 13y ago
  Interesting; does the id in the URL change?
- baddox 13y ago
  A really cool idea would be a site where people can submit anything they want with any title they want, and users' votes will determine how the stories get sorted. That way, the community could easily express and realize their preference for titles by upvoting the ones they prefer.
  - bobbles 13y ago
    The problem with a system with no moderation is that the abusers of the system have more time and incentive to abuse than the community does to moderate.
- deleted 13y ago
  [deleted]

sgtnasty 13y ago

I wish I could understand this.

Nursie 13y ago
What I'm getting from this is that - > under relativity fast things are heavier > electrons are fast, they actually have about a 23% weight boost > heavier electrons 'orbit' closer to the nucleus > the atomic size is then smaller than anticipated > this has a bunch of interesting effects on melting points, reactivity, colour/reflectivity etc, (especially of transition metals?) > this stuff has not always been well understood. It's been a long time since I studied chemistry, so I may be reading it wrong. It's pretty cool though :)
- VladRussian2 13y ago
  inter-disciplinary science of such effects http://en.wikipedia.org/wiki/Relativistic_quantum_chemistry http://en.wikipedia.org/wiki/Relativistic_quantum_chemistry

deleted 13y ago

[deleted]

mjfl 13y ago

There is another interesting Q/A on physics.stackexchange about why gold is... gold. http://physics.stackexchange.com/questions/72368/why-are-most-metals-gray-silver http://physics.stackexchange.com/questions/72368/why-are-mos...

minikites 13y ago
And here's an interesting story on why gold was destined to be used as currency: http://www.npr.org/blogs/money/2011/02/15/131430755/a-chemist-explains-why-gold-beat-out-lithium-osmium-einsteinium http://www.npr.org/blogs/money/2011/02/15/131430755/a-chemis...
- jameshart 13y ago
  Interesting that it misses what I always thought was the most important property of gold in this regard which is that it is (for a pre-technological society at least) completely unadulterable. It's the densest material you can readily obtain, without the ability to smelt platinum (whose melting point issues were mentioned in the article as a disqualifier for functioning as money). That means that I can't make a coin that matches both the size and the weight of a real gold coin out of anything other than gold. If you'd picked iron as the precious metal, I could fake an iron coin by mixing tin and lead together so the alloy's density matches iron's. But to make a fake gold coin without using gold, I need to mix something lighter than it with something heavier - and my options looking for something heavier are either in the platinum group, or are heavy radioisotopes like Uranium. All of which are probably sufficiently rare in a pre-technological society that they're worth more than their weight in gold anyway, so not much use as raw materials in a forgery. Density is destiny...?

dnautics 13y ago

Ok. So what is interesting here, is that chemists have long suspected this (to the point that this explanation was dogma to me as a grad student) but new paper gives it a fairly rigorously demonstrations from first principles in a less-handwavey fashion.

spuz 13y ago

Interestingly the actual melting point of Mercury (according to Wikipedia) is 234.3210K which is still a way off the 250K calculated by this study. I wonder how realistic is it to exactly calculate melting points of metals and other materials from first-principles?

shmageggy 13y ago
Well, it's an order of magnitude closer than the 355K that was predicted without accounting for relativity, and I think the point was that a melting point of 355K (82C) means it would be solid at room temperature, while 250K (-23C) means it is liquid at room temperature, so they can conclude it's the relativistic effect that's responsible for its weirdness. tl;dr: close enough.
Florin_Andrei 13y ago
It's a miracle they did it anyway. I still remember calculating the hydrogen atom back in college. It's a trivial case compared to mercury, yet it takes a surprising amount of scribbling. I assume they did all sorts of approximate models for mercury. An analytic, rigorous solution must be impossible.

andrewflnr 13y ago

If it's just about the electrons being pulled closer to the nucleus, why doesn't the effect apply nearly as much to it's neighbors on the periodic table?

wiredfool 13y ago
Because it's the one with full d orbitals as the outer electrons.
- VLM 13y ago
  To extend on wiredfools remarks, the effect of non-full means lots of electron sharing going on. But if they're full, the (smaller) effects of relativity are the only effects so they're dominant. The neighbors are non-full so the sharing they do is way more important level than relativity level effects.

evanb 13y ago

The explanation, as described in the article, is lacking, since it does not really explain why no other elements are liquid. The suggestion is that it is that the 6s orbital is full. Why don't other large-Z elements with filled p- or d- or f- orbitals also become liquids?

VLM 13y ago
TLDR is they do. The medium form answer is look at the periodic table. There's block of s (which don't count because other than H/He they are buried deep in the atom) and a block of d where the full ones do have ridiculous low melting points compared to neighbors (like Zinc, Cadmium, Mercury...) and a block of p shell where the full p shells are the well known noble gases which are liquid at really low temps and the block of f weirdos who don't matter. As for the f weirdos not mattering look at the electron configuration for something like Tb. Yes very nice that it has a peculiar collection of 4 level f shaped orbital electrons but I guess the more influential effect is the 5 level s and 5 level p and more importantly the 6 level s way out there in front of the mere 4 level f. Its kind of like D+D or pathfinder multiclass, oh, you have 2 levels of bard multiclassed into your level 10 sorcerer, well whatever, that bard isn't going to matter very much compared to the sorcerer level powers. So back to your question, the filled p make great gasses at room temp not mere liquids you are totally correct here, the filled d have really low melting points for metals like Hg being a liquid as discussed, and the filled f are weirdos who fool around with electron configurations at mere level 4 when the real chemical action is at level 6 so they don't matter (sorta) For a more correct, longer form answer someone else will have to step in.
- davvolun 13y ago
  Favorite analogy ever. Don't really know why the 4 level f shaped orbital electrons are a level 2 multiclassed bard and the two 5 level s/p and 6 level s are like a level 10 sorcerer, but that may be because I understand about 5 of the words at the beginning of this sentence. It's been a really long time since chemistry.
  - jjoonathan 13y ago

ttflee 13y ago

It seems quite bizarre that the introductory chemistry about elements is taught without the prerequisite knowledge of Schrödinger equation and special relativity in college.

akincisor 13y ago

Gallium melts not much higher than room temperature... Is that explained by orbitals as well?

cantrevealname 13y ago

> the electron approaches about 58% of the speed of light, and its mass increases to 1.23 times its rest mass Does this mean that as mercury is cooled to absolute zero, the electron will slow down and mercury will become lighter?

raverbashing 13y ago
No. You can't have an electron filling lower energy levels if they're already occupied. Also, I'm guessing what they mean by "electron speed" is actually electron energy.