5 ms·

Relativity behind mercury's liquidity (2013)

37 points by zeristor 6y ago

zeristor 6y ago
It seems this Wikipedia article on why Gold is yellow was posted a while back: https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry
zeristor 6y ago
So are even heavier elements more interesting. I would expect more coloured elements, more liquid elements at room temperature for heavier elements. Can the number of neutrons in an isotope make a big difference, there are a few elements which have a wide range of isotopic weights, if a property was quite delicate I’d expect such changes to be quite apparent, tricky for millisecond half lives.
- FreeFull 6y ago
  One thing that comes to mind is https://en.wikipedia.org/wiki/Kinetic_isotope_effect https://en.wikipedia.org/wiki/Kinetic_isotope_effect , although this seems to mostly affect elements that only have a few protons, like hydrogen or oxygen. Still, it adds up enough so that replacing most of the water in your body with heavy water (D₂O) would be fatal.. But, you'd have to drink exclusively heavy water for a long time to actually reach a toxic dose.
  - deleted 6y ago
    [deleted]
  - zeristor 6y ago
    Yes thanks for reminding me about Heavy Water ice, and how it sinks in a glass of water too. Also I have subscript envy, and shall scour the Internet as to how to do subscripts in HN.
    - FreeFull 6y ago
      I used the subscript 2 unicode character (U+2082). As far as I know, HN's formatting doesn't include anything to do subscripts. (At least, https://news.ycombinator.com/formatdoc https://news.ycombinator.com/formatdoc does not mention it.)
- radioactivist 6y ago
  Most of the properties of materials are from the charged pieces that make them up -- the protons and electrons. Since adding neutrons wouldn't change the number of electrons or protons other isotopes would be almost identical for the purposes of chemistry, light, etc. Some small differences might crop up in things that depend explicitly on the mass of the nucleus (e.g. sound propagation, density). But given adding a few neutrons in heavy nucleus is a change of order a percent or so in mass it isn't likely to be dramatic.
  - zeristor 6y ago
    My main question was are the only examples in Mercury, and Gold? AI, and Hg are next to each other on the periodic table, just on the metal / non-metal boundary, beneath them are the Rg, and Cn. Rg Roentgenium has a short half life, but seems to be tricky to make, it is expected to show some Relativistic properties though: https://en.m.wikipedia.org/wiki/Roentgenium https://en.m.wikipedia.org/wiki/Roentgenium Cn Copernicum, according to Wikipedia seems to show RQM effects it acting like a noble gas, albeit one with a half-life of at most 28s: https://en.m.wikipedia.org/wiki/Copernicium https://en.m.wikipedia.org/wiki/Copernicium If so why only these too? I’d expect there to be several others with mysterious properties too.
- deleted 6y ago
  [deleted]
throwaway_pdp09 6y ago
I understand electrons are a probability cloud but suddenly > The larger the nucleus gets the greater the electrostatic attraction and the faster the electrons have to move to avoid falling into it and now they're moving (and in this case, faster). So how does a particle with no attributable position move faster? This doesn't make sense.
- MockObject 6y ago
  It's a probability cloud of different possible locations, but also it's a probability distribution of different permitted possible speeds, as well. This probability distribution has a peak (a mode). When he writes "the faster the electrons have to move", he means this mode for a heavier nucleus is larger than that of a lighter nucleus. Please let me know if I'm not being clear enough.
  - throwaway_pdp09 6y ago
    Actually thanks, that's very clear at that level, however that leads to a further confusion (of mine) about what speed implies, that being that the electron is moving (obviously) from x to y, which apparently contradicts the probability cloud concept of probabilities of a position at instant x, and only for that instant. That is, if it's moving from x to y (because it has speed) then it's more likely to appear on some vector between x and y. Please feel free not to answer that question, as I may drag you down the rabbit hole - but if you can, I'd love to know.
    - analog31 6y ago
      On possible way to think about it, is to imagine a probability cloud of something else, but made of classical particles. For instance, all of the cell phones in Chicago. Someone like Google can probably compute an average position, such as maybe a center of mass, but also an average speed based on knowing the speeds of all the phones as they're carried about, driven in cars, etc. Now what we might have done in quantum mechanics class, without thinking too hard about the implications, is to assign mathematical functions to the things that we want to know about the electron using rules of thumb for how to turn functions of classical systems into corresponding functions of quantum systems. Then we apply the "what is your average speed" operator, and out pops a number. I didn't get very far past the basic quantum mechanics where we were able to compute stuff but were left on our own to speculate about the meaning of the philosophical implications. Then I joined an experimental research team where I was able to think my way through problems using electronics, vacuum pumps, and computer code. ;-)
peter_d_sherman 6y ago
>"In the 1960s, Pekka Pyykkö, now at University of Helsinki, Finland, discovered that gold’s colour was the result of relativistic effects. He showed that the lower energy levels of the 6s orbital of gold means that the energy required to excite an electron from the 5d band lies in the visible rather than UV range of light. This means that gold absorbs blue light, while reflecting yellow and red light, and it is this that gives the metal its characteristic hue."

37 points by zeristor 6y ago

It seems this Wikipedia article on why Gold is yellow was posted a while back: https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry

zeristor 6y ago

So are even heavier elements more interesting. I would expect more coloured elements, more liquid elements at room temperature for heavier elements. Can the number of neutrons in an isotope make a big difference, there are a few elements which have a wide range of isotopic weights, if a property was quite delicate I’d expect such changes to be quite apparent, tricky for millisecond half lives.

FreeFull 6y ago
One thing that comes to mind is https://en.wikipedia.org/wiki/Kinetic_isotope_effect https://en.wikipedia.org/wiki/Kinetic_isotope_effect , although this seems to mostly affect elements that only have a few protons, like hydrogen or oxygen. Still, it adds up enough so that replacing most of the water in your body with heavy water (D₂O) would be fatal.. But, you'd have to drink exclusively heavy water for a long time to actually reach a toxic dose.
- deleted 6y ago
  [deleted]
- zeristor 6y ago
  Yes thanks for reminding me about Heavy Water ice, and how it sinks in a glass of water too. Also I have subscript envy, and shall scour the Internet as to how to do subscripts in HN.
  - FreeFull 6y ago
    I used the subscript 2 unicode character (U+2082). As far as I know, HN's formatting doesn't include anything to do subscripts. (At least, https://news.ycombinator.com/formatdoc https://news.ycombinator.com/formatdoc does not mention it.)
radioactivist 6y ago
Most of the properties of materials are from the charged pieces that make them up -- the protons and electrons. Since adding neutrons wouldn't change the number of electrons or protons other isotopes would be almost identical for the purposes of chemistry, light, etc. Some small differences might crop up in things that depend explicitly on the mass of the nucleus (e.g. sound propagation, density). But given adding a few neutrons in heavy nucleus is a change of order a percent or so in mass it isn't likely to be dramatic.
- zeristor 6y ago
  My main question was are the only examples in Mercury, and Gold? AI, and Hg are next to each other on the periodic table, just on the metal / non-metal boundary, beneath them are the Rg, and Cn. Rg Roentgenium has a short half life, but seems to be tricky to make, it is expected to show some Relativistic properties though: https://en.m.wikipedia.org/wiki/Roentgenium https://en.m.wikipedia.org/wiki/Roentgenium Cn Copernicum, according to Wikipedia seems to show RQM effects it acting like a noble gas, albeit one with a half-life of at most 28s: https://en.m.wikipedia.org/wiki/Copernicium https://en.m.wikipedia.org/wiki/Copernicium If so why only these too? I’d expect there to be several others with mysterious properties too.
deleted 6y ago
[deleted]

throwaway_pdp09 6y ago

I understand electrons are a probability cloud but suddenly > The larger the nucleus gets the greater the electrostatic attraction and the faster the electrons have to move to avoid falling into it and now they're moving (and in this case, faster). So how does a particle with no attributable position move faster? This doesn't make sense.

MockObject 6y ago
It's a probability cloud of different possible locations, but also it's a probability distribution of different permitted possible speeds, as well. This probability distribution has a peak (a mode). When he writes "the faster the electrons have to move", he means this mode for a heavier nucleus is larger than that of a lighter nucleus. Please let me know if I'm not being clear enough.
- throwaway_pdp09 6y ago
  Actually thanks, that's very clear at that level, however that leads to a further confusion (of mine) about what speed implies, that being that the electron is moving (obviously) from x to y, which apparently contradicts the probability cloud concept of probabilities of a position at instant x, and only for that instant. That is, if it's moving from x to y (because it has speed) then it's more likely to appear on some vector between x and y. Please feel free not to answer that question, as I may drag you down the rabbit hole - but if you can, I'd love to know.
  - analog31 6y ago
    On possible way to think about it, is to imagine a probability cloud of something else, but made of classical particles. For instance, all of the cell phones in Chicago. Someone like Google can probably compute an average position, such as maybe a center of mass, but also an average speed based on knowing the speeds of all the phones as they're carried about, driven in cars, etc. Now what we might have done in quantum mechanics class, without thinking too hard about the implications, is to assign mathematical functions to the things that we want to know about the electron using rules of thumb for how to turn functions of classical systems into corresponding functions of quantum systems. Then we apply the "what is your average speed" operator, and out pops a number. I didn't get very far past the basic quantum mechanics where we were able to compute stuff but were left on our own to speculate about the meaning of the philosophical implications. Then I joined an experimental research team where I was able to think my way through problems using electronics, vacuum pumps, and computer code. ;-)

peter_d_sherman 6y ago

>"In the 1960s, Pekka Pyykkö, now at University of Helsinki, Finland, discovered that gold’s colour was the result of relativistic effects. He showed that the lower energy levels of the 6s orbital of gold means that the energy required to excite an electron from the 5d band lies in the visible rather than UV range of light. This means that gold absorbs blue light, while reflecting yellow and red light, and it is this that gives the metal its characteristic hue."