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Author: Subject: Aluminum a rare earth metal ?
metalresearcher
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[*] posted on 29-8-2021 at 11:08
Aluminum a rare earth metal ?


In an old (1919) German chemistry textbook of W.Ostwald "Grundlinien der anorganischen Chemie" (Fundamentals of inorganic chemistry) I found an interesting chapter about Aluminum. There is a subchapter called "583, Die anderen Erdmetalle" (The other Earth metals) and they mention Scandium, Yttrium and the Rare Earths (#57-71). Now we consider Al als group 13 with Ga, In, Tl, but the properties of Al metal are more like the RE metals rather than the higher group 13 elements.

Another interesting fact (not attached) is that they mention 'Ammonium' at the alkali metals, due to the similarity of NH4+ salts to the alkali metal salts, so, indeed 'ammonium' is a virtual alkali metal.

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[*] posted on 29-8-2021 at 11:19


Depends on how you define "rare earth". Keep in mind that the definitions and classifications of the elements are often arbitrary (we have to pick *somewhere* to draw the division lines), and it often isn't particularly useful to argue over definitions. I myself was shocked to learn (after teaching intro chem for a decade) that lanthanum was considered a lanthanoid/lanthanide (which I consider to mean "lanthanum-like", and something isn't merely *like* itself, it IS itself).

It's just like where you draw the line between organic compounds and inorganic compounds containing carbon. Nobody considers calcium carbonate to be organic. What about calcium oxalate? Acetate? Benzoate?




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[*] posted on 29-8-2021 at 15:00


To me, conceptually, Al seems to fit in with In/Ga because their halides are Lewis acids, while scandium trihalides are weakly acidic and Y/La halides are essentially nonacidic. B/Al/Ga/In hydrides can be made by hydrogenation of the chlorides and form tetrahydridometallates, while ScH3 is incredibly unstable and lithium scandium hydride does not seem to be described. Yttrium meanwhile reacts with hydrogen gas to form hydrides which are apparently thermodynamically stable, a behavior not seen in any poor metal (and all of their hydrides are >0 H_f).



[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 30-8-2021 at 00:38


I have the same book (I really like it), but it is an old book and insights have changed since then. Indeed, ammonium is mentioned as a pseudometal and this is based on the very interesting observation that a solution of NH4 in mercury can be made by electrolysis of a solution of an ammonium salt with a mercury cathode. This ammonium amalgam slowly decomposes, giving ammonia, hydrogen and mercury, so this amalgam is not very stable, but the fact that it can be prepared and kept around for a while is interesting. I, however, would not call this a pseudometal for this reason. Nowadays we know of more compounds with metals, which have similar behavior (e.g. atomic hydrogen with certain metals and some amines also show similar behavior).

What I find most striking in such old books is the tendency to give explanations of phenomena, with exact stoichiometries of all kinds of compounds. Nowadays we know there are many compounds which have no exact stoichiometry and in fact form a continuum or range of compounds. Many transition metals form sulfides, oxides and phosphides with a ranmge of stoichiometries and we even know of compounds which can have a range of alkali metal ions in them, such as the molybdenum bronzes (which can be considered as MoO3 with additional alkali ions added, so their formula is (for the potassium variation) KxMoO3, where x can be anything between 0 and appr. 0.5). Such compounds usually are mixed oxidation state compounds, e.g. the molybdenum bronzes have Mo in oxidation state +6 and Mo in oxidation state +5 in a ratio, depending on how many K(+) ions are incorporated in the crystal lattice. The book does its best to explain such compounds and sometimes comes up with weird formulae, with large integer ratios of elements in the compounds.

I love these old books, mainly because of their precise and complete description of all kinds of observations, which are not given in new books anymore. Sometimes you find a very interesting thing in such books, which now is totally forgotten or even obscure. A similar thing I observed in the old books of Holleman, from the start of the 20th century.




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metalresearcher
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[*] posted on 30-8-2021 at 02:21


woelen: I have the same Holleman book (a green one, from 1944) which is also very nice.

In the Sodium chapter in the Ostwald book, they don't have an explanation of the yellow flame color. Presumably the change in energy levels was not known by then.

I have downloaded more old books (but then as PDF and not in paper obviously) from late 19th and early 20th century. Really very nice. The book 'Henri Moissan - The Electric arc furnace' is also very nice, he describes exposing many substances to very high arc temperatures and what happens.
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[*] posted on 30-8-2021 at 06:22


Quote: Originally posted by metalresearcher  
In the Sodium chapter in the Ostwald book, they don't have an explanation of the yellow flame color. Presumably the change in energy levels was not known by then.
People didn’t know that electrons existed until the end of the 19th century, and didn’t come close to a modern understanding of atomic structure and bonding until the 1920s. Considering that, it’s amazing, looking at it from a modern perspective, that people were able to figure out so much about chemistry before that, while being so in the dark on the fundamentals. But ultimately, what we take for granted as fundamentals today are relatively new concepts, and the early chemists were able to learn a lot by approaching chemistry from a completely different perspective that is hard to grasp today



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[*] posted on 30-8-2021 at 07:14




Quote: Originally posted by clearly_not_atara  
To me, conceptually, Al seems to fit in with In/Ga because their halides are Lewis acids, while scandium trihalides are weakly acidic and Y/La halides are essentially nonacidic. B/Al/Ga/In hydrides can be made by hydrogenation of the chlorides and form tetrahydridometallates, while ScH3 is incredibly unstable and lithium scandium hydride does not seem to be described. Yttrium meanwhile reacts with hydrogen gas to form hydrides which are apparently thermodynamically stable, a behavior not seen in any poor metal (and all of their hydrides are >0 H_f).


Another chemical behavior is that Al, Ga, In hydroxides are soluble in solutions of alkali hydroxides, while Sc, Y, La hydroxides aren't.




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