In chemistry class, we discussed how metallic bonding occurs when metals lose electrons and become cations while the lose electrons become delocalized electrons and bind the metal cations. These electrons are then free to flow around the metal cations. But could the metal be replaced with an ammonium cation instead? (Or any other polyatomic cation, but we only learn ammonium and I'm not aware of any others minus hydronium which doesn't exist out of a solution.) Would the electrons still be free? How would you make it? And how could you prevent the following from occurring? $$\ce{2NH4+ + 2e- -> 2NH3 + H2}$$
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$\begingroup$ There are phases of solvated electrons in liquid ammonia that are metal-like. Thought these are created by dissolving metals like sodium in liquid ammonia. $\endgroup$– matt_blackCommented Dec 22, 2016 at 23:08
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$\begingroup$ Hydronium ion can be isolated in salts from very strong acids, like the perchlorate $\ce {H3OClO4}$. But you would not want to mess with it. $\endgroup$– Oscar LanziCommented Mar 29, 2017 at 1:54
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2 Answers
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A nomenclature note: conventionally, in chemistry "a metal" is an element (such as a transition metal or alkali metal). If what you're talking about is a substance that behaves as a metal, that's typically referred to as metallic, like metallic glasses.
Therefore, I would rephrase your question as "Can metallic ammonium exist?" - in fact, this has been a question for quite awhile. From what I've read, there's a theoretical basis that it should be possible at given temperatures and pressures, but it hasn't been experimentally observed. The papers I was reading were from the 50s-70s, so I'll keep looking for more recent information.
Solvated electrons are slightly related, in that there is a "free" electron, and this was in fact originally documented in liquid ammonia.
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We do know that ammonium "molecules" can be incorporated into an amalgam with mercury like many metallic elements (http://www.sciencemadness.org/talk/viewthread.php?tid=12906; a technical reference is given by for example 1). It must be chilled to retain stability, but it is a real material. As with amalgams of actual metallic elements, ammonium amalgam is metallically bonded, so the ammonium exists as cations, with the compensating electrons intermingled with the other conducting electrons from the mercury.
Reference
- Reedy, J.H. (October 1, 1929). "Lecture demonstration of ammonium amalgam". Journal of Chemical Education. 6 (10): 1767. Bibcode:1929JChEd...6.1767R. https://doi.org/10.1021/ed006p1767
answered Mar 29, 2017 at 1:44