An experiment suggested by a PhD student may rewrite chemistry textbooks
phys.org
phys.org
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
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
Behind a paywall...
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.
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.
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
0) https://www.reference.com/science/alkali-metals-react-water-...
Putting a small lump in a bucket outdoors using a rope-activated rig sounds pretty reasonable, though.
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.
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.
"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."
The article is incorrect on this. Some non-metals can conduct electricity.
Any substance that contains free electricity carriers will conduct electricity. Examples of electrical conductors that are not metals: 1. Liquid electrolytes 2. Solid electrolytes 3. Semiconductors 4. Ionized gases 5. Vacuum in which electrons or ions have been injected by some means All of the above are used in common devices.
The metals are solid or liquid electrical conductors which contain free electrons that are intrinsic, i.e. not produced by various methods, like in semiconductors.
Besides free electrons, metal have a second characteristic, which was used already in the 18th century to distinguish metals from semi-metals.
While this distinction is seldom mentioned nowadays, it remains useful. Metals have both free electrons and a crystal structure that allows plastic deformation (i.e. with high coordination number), while semi-metals have free electrons, but they have a crystal structure that does not allow plastic deformation, i.e. they are fragile. Examples of semi-metals: graphite, antimony, bismuth.
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.
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.
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.
> "He said, 'I don't have funding for your idea but if you come over here we can write a funding proposal together,'" said McMullen, who at the time was finishing up his undergraduate studies...
> Bradforth not only helped McMullen secure funding, prioritizing it for National Science Foundation support over continuing other projects, but he also cobbled together an international team of scientists and arranged his sabbatical to oversee and participate in the main experiments. He also became McMullen's Ph.D. adviser.
Man you gotta love such an awesome prof
This seems like it could be a massive problem with research. It means that grad students don't get to develop their own ideas, they have to work on their advisors research. Admittedly there are a lot of people who have trouble coming up with their own ideas, but this basically seems like a suppression of independent thinking.
The independent thinking here got funded. That's not evidence of suppression - quite the opposite, in fact.
I imagine you're mostly funding humans (who have provided a rough, or even detailed plan; which will likely be subject to modification or analysis as the project evolves), in which case experience is a strong heuristic.
And presumably, if you can't convince any possible advisors that your research is "potentially interesting", it seems unlikely you'd convince the funding department, or even should be able to convince them (who presumably have limited knowledge of the precise area of focus -- I imagine they rely on the deeper specialist input).
Of course, if you can convince an advisor that its potentially interesting, there should ideally be nothing stopping further development (eg no one should be claiming that it originated from a student, so it can't possibly be valid -- it's been validated by the advisor, so that's the heuristic to now beat)
https://blogs.sciencemag.org/pipeline/archives/2020/06/24/am...
> Banting was no expert in the field of carbohydrate metabolism, so when he requested laboratory space and facilities from Professor John James Rickard Macleod, Head of Physiology at the University of Toronto, the esteemed physiologist was at first reluctant.
> However, Banting’s persistence and the possibility of more reliable results persuaded MacLeod to donate laboratory space. While tying up the pancreas to make it break down was not a new investigative tool, the idea of isolating islets due to their slower degeneration was of keen interest to Macleod.
https://www.medicalnewstoday.com/articles/323774#development
The scientists cooled ammonia—normally a gas at room temperature—to minus 33 C to liquify it and then added, in separate experiments, the alkali metals lithium, sodium and potassium.
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."