> 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.<p>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.<p>> 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.<p>This is a Birch Reduction, which was first reported in 1944 based on earlier research:<p><a href="https://en.wikipedia.org/wiki/Birch_reduction#History" rel="nofollow">https://en.wikipedia.org/wiki/Birch_reduction#History</a><p>From the article:<p>> 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.<p>Maybe there's something interesting here, but you sure can't tell from the article.<p>There's no link to primary research anywhere that I can see. There's really no excuse for this.<p>Edit: found the paper at the bottom:<p><a href="https://science.sciencemag.org/content/368/6495/1086" rel="nofollow">https://science.sciencemag.org/content/368/6495/1086</a><p>Behind a paywall...