6 ms·

> Intuition suggests that metals are dense, and while that bears true for some (think gold or lead), it fails to hold up for others. For example, lithium—common

by aazaa 6y ago

> Intuition suggests that metals are dense, and while that bears true for some (think gold or lead), it fails to hold up for others. For example, lithium—commonly used in batteries—floats on water. Some metals are hard, such as titanium, yet others yield easily to pressure, including indium and aluminum. How about melting temperature? Platinum melts at more than 1,700 degrees Celsius (3,200 F), but mercury is a liquid well below zero. What makes a metal a metal has been known for many decades. It's the tendency to donate electrons. The article makes it sound like this is some kind of mystery that textbooks don't yet explain. Not so by a long shot. > In these solutions, electrons from the alkali metal initially become trapped in the gaps between ammonia molecules. This creates what scientists call 'solvated electrons,' which are highly reactive but stabilized in the ammonia. These solutions have a characteristic blue color. But given enough solvated electrons, the whole liquid turns bronze and, in essence, becomes a metal while remaining liquid. This is a Birch Reduction, which was first reported in 1944 based on earlier research: https://en.wikipedia.org/wiki/Birch_reduction#History https://en.wikipedia.org/wiki/Birch_reduction#History From the article: > The results showed that, at low concentrations, solvated electrons were more easily dislodged from the solution by the interaction with the X-rays, giving a simple energy pattern. At higher concentrations, though, the energy pattern suddenly developed a sharp band edge, indicating the solution was behaving as a metal would. Maybe there's something interesting here, but you sure can't tell from the article. There's no link to primary research anywhere that I can see. There's really no excuse for this. Edit: found the paper at the bottom: https://science.sciencemag.org/content/368/6495/1086 https://science.sciencemag.org/content/368/6495/1086 Behind a paywall...

mirimir 6y ago
Here: https://sci-hub.st/10.1126/science.aaz7607 https://sci-hub.st/10.1126/science.aaz7607 And yeah, TFA is a little lame. I laughed at "lithium...floats on water". It's true that it's less dense, but "float" is a huge understatement. That is, it skitters, like water on a hot frying pan. But, I guess because it's less dense, it doesn't detonate as often as sodium or potassium do.
- nl 6y ago
  > It's true that it's less dense, but "float" is a huge understatement. That is, it skitters, like water on a hot frying pan. No, if you wrapped it in some impermeable coating so it couldn't react with water it would still float. > But, I guess because it's less dense, it doesn't detonate as often as sodium or potassium do. It doesn't "detonate as often" because it is less reactive than sodium and potassium because it is less likely to lose it's outer electron because that outer electron is closer to the nucleus. That also means it is denser.
  - mirimir 6y ago
    OK, sure. But TFA doesn't mention any coating. I found a resource that corroborates what I said about behavior on water.[0] But it doesn't get into why that is. And about density and electronegativity: g/cm^3 χ (Pauling) 1st ionization energy (kJ/mol) Li 0.535 0.98 520 Na 0.968 0.93 496 K 0.856 0.84 419 The difference in density is larger than that for electronegativity and 1st ionization energy. But yes, all three arguably play a role. Still, for Li vs Na, density seems like the major factor. 0) https://www.reference.com/science/alkali-metals-react-water-b7495b0b4fb484e2 https://www.reference.com/science/alkali-metals-react-water-...
  - jtbayly 6y ago
    Lithium is denser then sodium?
- cbhl 6y ago
  My high school chemistry teacher lamented that he had fond memories of taking a lump of a metal (sodium, potassium) and watching the fireworks with his students when they threw it in a pond out back. These days, he has to settle for taking a small sliver and dropping it into a beaker of water behind a safety shield.
  - mnw21cam 6y ago
    My school teacher chucked a golf-ball-size lump of sodium into the school swimming pool, then declared a wish to see the face of the guy who tests the pH of the pool the next morning.
URSpider94 6y ago
Reading the abstract from Science, they were able to visualize the transition of the band structure of the dissolved electrons from an insulator with discrete energy states to a conductor with a wide valence band and a Fermi level, just like a metal. This is exactly what basic theory predicts, but I can’t think of another system that can be tweaked like this to demonstrate that transition so cleanly. Given the weak interaction between the electrons and the ammonia, it can probably be modeled fairly simply, which is nice.
- twic 6y ago
  That explanation makes sense! Some selected highlights from the paper, saying, i think, the same thing, in a little more depth (PE = photoelectron, PES = photoelectron spectroscopy): > The nature of the metallic transition in both liquid and crystalline alkali metal–ammonia systems, directly evidenced by an orders-of-magnitude increase in electrical conductivity, has puzzled researchers for decades and is not yet understood in molecular detail. > There is thus a clear need for a direct PES investigation of excess ammoniated electrons that would cover both the electrolyte and metallic regimes. We have recently overcome a critical obstacle in collecting PEs from a volatile polar refrigerated liquid. > This work has paved the way for PES investigations mapping the electrolyte-to-metal transition through the study of liquid alkali metal–ammonia solutions of increasing concentrations, as reported here. > The present study shows that the electrolyte-to-metal transition in increasingly concentrated alkali metal–liquid ammonia solutions is a gradual process rather than an abrupt first-order transition, which is in line with previous suggestions. From the molecular point of view, this transition may be understood in a simplified way as gradual coalescence of individual solvated electrons and dielectrons upon increasing alkali metal doping, with the metallic behavior appearing around the percolation threshold.
deleted 6y ago
[deleted]
msie 6y ago
From the article: "Intuition suggests that metals are dense, and while that bears true for some (think gold or lead), it fails to hold up for others. For example, lithium—commonly used in batteries—floats on water. Some metals are hard, such as titanium, yet others yield easily to pressure, including indium and aluminum. How about melting temperature? Platinum melts at more than 1,700 degrees Celsius (3,200 F), but mercury is a liquid well below zero. Many other definitions of 'metal-hood' suffer similar contradictions, but only metals are able to conduct electricity. Conduction, unlike density or hardness, is an inherent property of all metals." From the article: "In these solutions, electrons from the alkali metal initially become trapped in the gaps between ammonia molecules. This creates what scientists call 'solvated electrons,' which are highly reactive but stabilized in the ammonia. These solutions have a characteristic blue color. But given enough solvated electrons, the whole liquid turns bronze and, in essence, becomes a metal while remaining liquid. Solvated electrons have proven to be important to organic chemists. Through a reaction called the "Birch reduction," named after chemist Arthur Birch, they were key to synthesizing many important compounds and led to the manufacture of oral contraceptives in the 1950s."
- aeternum 6y ago
  >only metals are able to conduct electricity The article is incorrect on this. Some non-metals can conduct electricity.
  - mianos 6y ago
    Quite a lot of non metals can conduct electricity. Even Oxygen has a solid phase (ζ-phase <- hope that renders), where oxygen is pretty much a conducting metal. Edit: ps, if you compress it more and cool it, even oxygen becomes a super conductor. This might confuse those guys.
  - snowwrestler 6y ago
    Almost anything will conduct electricity if you crank the voltage high enough... :-0
- adrian_b 6y ago
raverbashing 6y ago
The video is more informative of their actual results
Torkel 6y ago
Yeah, I was also disappointed in this story. Shallow and bad explanation and after reading it I am still none the wiser as to in what way those textbooks would be in need of rewriting.
rubidium 6y ago
This is classic hn dismissalism. The news article isn’t great, but it did a better job than you give it credit for in stating the significance. It linked the paper and talked about birch reactions. I don’t read Science (the journal) regularly, but news articles like this function as flags for “there may be an new paper worth reading” so I go get it from everyone’s favorite repository of scientific papers. That’s the value. If you want to critique the state of scientific news writing that’s fine but realize you’re just whining. The fact that it’s about science news isn’t that much different than political news.
- willis936 6y ago
  >dismissalism You can put -ism at the end of any word. In most cases it will just demonstrate an agenda-driven dichotomy. Criticizing a culture of critique requires a culture of critique. So no, HN does not have a problem here and the OP is not whining. This is the system working as intended.
  - turbonoobie 6y ago
    imsisms is becoming a strange problem I have yet to figure out how to deal with in my day-to-day conversations.
- tomp 6y ago
  If you put a title "may rewrite chemistry books" on top of an article about "a new paper worth reading", you're doing it wrong. Classical click-bait at best, fake news at worst.
  - lallysingh 6y ago
    If it causes one line of chem textbooks to change, it's fit the claim. Not a very high standard, just sexy sounding.
    - snakeboy 6y ago
      "rewrite" obviously implies a much larger change, in my opinion. After passing a constitutional amendment, would it not be misleading to declare "The US rewrites the constitution" ? If a 2nd edition of a novel includes a new preface, it would be misleading to advertise the book as "re-written". You see it as "sexy sounding", I see it as intentionally misleading about the significance of the result.
cashsterling 6y ago
My PhD thesis was in surface science and solid-state physics and I did a lot of UV photoelectron spectroscopy. I can tell you that this an extremely interesting group of results. And it is continuing to muddy the waters as to what constitutes a metallic state.

by aazaa 6y ago

mirimir 6y ago

Here: https://sci-hub.st/10.1126/science.aaz7607 https://sci-hub.st/10.1126/science.aaz7607 And yeah, TFA is a little lame. I laughed at "lithium...floats on water". It's true that it's less dense, but "float" is a huge understatement. That is, it skitters, like water on a hot frying pan. But, I guess because it's less dense, it doesn't detonate as often as sodium or potassium do.

nl 6y ago
> It's true that it's less dense, but "float" is a huge understatement. That is, it skitters, like water on a hot frying pan. No, if you wrapped it in some impermeable coating so it couldn't react with water it would still float. > But, I guess because it's less dense, it doesn't detonate as often as sodium or potassium do. It doesn't "detonate as often" because it is less reactive than sodium and potassium because it is less likely to lose it's outer electron because that outer electron is closer to the nucleus. That also means it is denser.
- mirimir 6y ago
  OK, sure. But TFA doesn't mention any coating. I found a resource that corroborates what I said about behavior on water.[0] But it doesn't get into why that is. And about density and electronegativity: g/cm^3 χ (Pauling) 1st ionization energy (kJ/mol) Li 0.535 0.98 520 Na 0.968 0.93 496 K 0.856 0.84 419 The difference in density is larger than that for electronegativity and 1st ionization energy. But yes, all three arguably play a role. Still, for Li vs Na, density seems like the major factor. 0) https://www.reference.com/science/alkali-metals-react-water-b7495b0b4fb484e2 https://www.reference.com/science/alkali-metals-react-water-...
- jtbayly 6y ago
  Lithium is denser then sodium?
cbhl 6y ago
My high school chemistry teacher lamented that he had fond memories of taking a lump of a metal (sodium, potassium) and watching the fireworks with his students when they threw it in a pond out back. These days, he has to settle for taking a small sliver and dropping it into a beaker of water behind a safety shield.
- mnw21cam 6y ago
  My school teacher chucked a golf-ball-size lump of sodium into the school swimming pool, then declared a wish to see the face of the guy who tests the pH of the pool the next morning.

URSpider94 6y ago

Reading the abstract from Science, they were able to visualize the transition of the band structure of the dissolved electrons from an insulator with discrete energy states to a conductor with a wide valence band and a Fermi level, just like a metal. This is exactly what basic theory predicts, but I can’t think of another system that can be tweaked like this to demonstrate that transition so cleanly. Given the weak interaction between the electrons and the ammonia, it can probably be modeled fairly simply, which is nice.

twic 6y ago
That explanation makes sense! Some selected highlights from the paper, saying, i think, the same thing, in a little more depth (PE = photoelectron, PES = photoelectron spectroscopy): > The nature of the metallic transition in both liquid and crystalline alkali metal–ammonia systems, directly evidenced by an orders-of-magnitude increase in electrical conductivity, has puzzled researchers for decades and is not yet understood in molecular detail. > There is thus a clear need for a direct PES investigation of excess ammoniated electrons that would cover both the electrolyte and metallic regimes. We have recently overcome a critical obstacle in collecting PEs from a volatile polar refrigerated liquid. > This work has paved the way for PES investigations mapping the electrolyte-to-metal transition through the study of liquid alkali metal–ammonia solutions of increasing concentrations, as reported here. > The present study shows that the electrolyte-to-metal transition in increasingly concentrated alkali metal–liquid ammonia solutions is a gradual process rather than an abrupt first-order transition, which is in line with previous suggestions. From the molecular point of view, this transition may be understood in a simplified way as gradual coalescence of individual solvated electrons and dielectrons upon increasing alkali metal doping, with the metallic behavior appearing around the percolation threshold.

deleted 6y ago

[deleted]

msie 6y ago

From the article: "Intuition suggests that metals are dense, and while that bears true for some (think gold or lead), it fails to hold up for others. For example, lithium—commonly used in batteries—floats on water. Some metals are hard, such as titanium, yet others yield easily to pressure, including indium and aluminum. How about melting temperature? Platinum melts at more than 1,700 degrees Celsius (3,200 F), but mercury is a liquid well below zero. Many other definitions of 'metal-hood' suffer similar contradictions, but only metals are able to conduct electricity. Conduction, unlike density or hardness, is an inherent property of all metals." From the article: "In these solutions, electrons from the alkali metal initially become trapped in the gaps between ammonia molecules. This creates what scientists call 'solvated electrons,' which are highly reactive but stabilized in the ammonia. These solutions have a characteristic blue color. But given enough solvated electrons, the whole liquid turns bronze and, in essence, becomes a metal while remaining liquid. Solvated electrons have proven to be important to organic chemists. Through a reaction called the "Birch reduction," named after chemist Arthur Birch, they were key to synthesizing many important compounds and led to the manufacture of oral contraceptives in the 1950s."

aeternum 6y ago
>only metals are able to conduct electricity The article is incorrect on this. Some non-metals can conduct electricity.
- mianos 6y ago
  Quite a lot of non metals can conduct electricity. Even Oxygen has a solid phase (ζ-phase <- hope that renders), where oxygen is pretty much a conducting metal. Edit: ps, if you compress it more and cool it, even oxygen becomes a super conductor. This might confuse those guys.
- snowwrestler 6y ago
  Almost anything will conduct electricity if you crank the voltage high enough... :-0
adrian_b 6y ago

raverbashing 6y ago

The video is more informative of their actual results

Torkel 6y ago

Yeah, I was also disappointed in this story. Shallow and bad explanation and after reading it I am still none the wiser as to in what way those textbooks would be in need of rewriting.

rubidium 6y ago

This is classic hn dismissalism. The news article isn’t great, but it did a better job than you give it credit for in stating the significance. It linked the paper and talked about birch reactions. I don’t read Science (the journal) regularly, but news articles like this function as flags for “there may be an new paper worth reading” so I go get it from everyone’s favorite repository of scientific papers. That’s the value. If you want to critique the state of scientific news writing that’s fine but realize you’re just whining. The fact that it’s about science news isn’t that much different than political news.

willis936 6y ago
>dismissalism You can put -ism at the end of any word. In most cases it will just demonstrate an agenda-driven dichotomy. Criticizing a culture of critique requires a culture of critique. So no, HN does not have a problem here and the OP is not whining. This is the system working as intended.
- turbonoobie 6y ago
  imsisms is becoming a strange problem I have yet to figure out how to deal with in my day-to-day conversations.
tomp 6y ago
If you put a title "may rewrite chemistry books" on top of an article about "a new paper worth reading", you're doing it wrong. Classical click-bait at best, fake news at worst.
- lallysingh 6y ago
  If it causes one line of chem textbooks to change, it's fit the claim. Not a very high standard, just sexy sounding.
  - snakeboy 6y ago
    "rewrite" obviously implies a much larger change, in my opinion. After passing a constitutional amendment, would it not be misleading to declare "The US rewrites the constitution" ? If a 2nd edition of a novel includes a new preface, it would be misleading to advertise the book as "re-written". You see it as "sexy sounding", I see it as intentionally misleading about the significance of the result.

cashsterling 6y ago

My PhD thesis was in surface science and solid-state physics and I did a lot of UV photoelectron spectroscopy. I can tell you that this an extremely interesting group of results. And it is continuing to muddy the waters as to what constitutes a metallic state.