Talk:Cerium

Tarnishes rapidly or slowly?
"Immediately after lanthanum, the 4f orbitals suddenly contract and are lowered in energy to the point that they participate readily in chemical reactions;"

Isn't this the exact opposite of what you want to say? The lanthanide contraction makes the 4f orbitals less likely to participate in chemical reactions, not more likely,72.200.200.2 (talk) 02:31, 5 April 2019 (UTC)
 * Well, I have corrected it since then (actually it happens already at La, not after La), but the point is correct: up till barium 4f is too high up to participates. At the early lanthanides it contracts and is lowered to the point that allows ready participation. Then as you progress through the lanthanide series they contract further than that and it becomes harder and harder to use them until ytterbium. At lutetium it becomes impossible. Double sharp (talk) 12:38, 26 January 2021 (UTC)

How hard is cerium? It cannot simultaneously be soft enough to cut with a knife and have a hardness similar to silver.
In the first paragraph I read: and it is soft enough to be cut with a steel kitchen knife

And in the "Physical" section I read: It is a ductile metal with a hardness similar to that of silver. I know silver cannot be cut with a knife. This statement has a credible citation labelled with the number 5.

I don't personally have any metallic cerium to try, but one or the other of these statements is true, but not both. I would tend to go with the one that has the citation, rather than the one labelled "citation needed". — Preceding unsigned comment added by Frostybeard (talk • contribs) 08:20, 22 January 2022 (UTC)

Section on Ce+4 not existing
I've removed this section: Despite the common name of cerium(IV) compounds, the Japanese spectroscopist Akio Kotani wrote "there is no genuine example of cerium(IV)". The reason for this can be seen in the structure of ceria itself, which always contains some octahedral vacancies where oxygen atoms would be expected to go and could be better considered a non-stoichiometric compound with chemical formula CeO2−x. Furthermore, each cerium atom in ceria does not lose all four of its valence electrons, but retains a partial hold on the last one, resulting in an oxidation state between +3 and +4. Even supposedly purely tetravalent compounds such as CeRh3, CeCo5, or ceria itself have X-ray photoemission and X-ray absorption spectra more characteristic of intermediate-valence compounds. The 4f electron in cerocene,, is poised ambiguously between being localized and delocalized and this compound is also considered intermediate-valent. because the sources do not appear to endorse it. And I can't find the opening quote anywhere. Jo-Jo Eumerus (talk) 21:27, 23 January 2022 (UTC)
 * Pinging Double Sharp who added this section a few years ago; perhaps they can clarify. Jo-Jo Eumerus (talk) 21:31, 23 January 2022 (UTC)
 * It is right there. From the transcript in the RSC podcast: Indeed the great Japanese spectroscopist Akio Kotani once wrote that 'there is no genuine example of Cerium 4'. (That's how you say "Ce(IV)" out loud; presumably whoever wrote the transcript was not aware of this.) For ceria, we have from that source: Ceria is also very hard which has made it a useful roche or polish for lens. If you happen to want to grind or polish your own telescope, then cerium dioxide is probably what you will use. But what makes the oxide really interesting is it misbehaves. Although the formula may appear to be CeO2, one cerium 2 oxygens in reality the compound always has slightly less than 2 oxygens; the surface is peppered with defects, gaps where an oxygen atom should be and the degree of imperfection varies.
 * For cerocene, the Nature source reads Another fun aspect of element 58 engendered by its redox activity is the somewhat unconventional and controversial electronic structures of its compounds, such as cerocene (Ce(C8H8)2), an 8-fold symmetric, eclipsed sandwich complex. The most accurate picture of the valence at its cerium cation has remained somewhat ambiguous. Energy decomposition analysis suggests a strong ionic interaction between the cerium centre and each cyclooctatetraene ring, and X-ray absorption spectroscopy indicates that cerocene has a ground state that is strongly multiconfigurational — so much so that the compound is now described as 'intermediate valent'. It is trapped between configurations of Ce(III) and Ce(IV) character that are quantum-mechanically admixed and comprise a strongly stabilized open-shell singlet ground state. ... The simultaneous local/non-local character of the 4f-electron in cerocene is reminiscent of f-element superconductors' behaviour, and investigations on cerium compounds can provide insight on how local behaviour gives rise to exotic materials properties. I'd do the same for the last source about the intermetallics, but I'd have to quote quite a lot of it.
 * In fairness, I cannot find where Kotani originally wrote that. However, I somehow doubt the Royal Society of Chemistry would've made it completely up. Double sharp (talk) 22:00, 23 January 2022 (UTC)
 * Double sharp (talk) 22:13, 23 January 2022 (UTC)
 * Thanks for solving this; the problem with using audio sources is that they are harder to use. I am not sure that I would interpret the sources as implying Furthermore, each cerium atom in ceria does not lose all four of its valence electrons, but retains a partial hold on the last one, resulting in an oxidation state between +3 and +4, however; as far as I know a non stoichiometric compound is a different thing from "partial hold" and -ocene compounds to my understanding often have charge-valence peculiarities. Incidentally, even after solving this issue I see there are other uncited sentences, stubby paragraphs and unsourced paragraphs here. Perhaps this should be sent to a good article review. Jo-Jo Eumerus (talk) 10:21, 24 January 2022 (UTC)
 * That bit is in the RSC podcast too: But if you take an even closer look at Ceria it becomes more confusing. At first sight it looks like a no-brainer. Cerium looses 4 electrons handing them over to the surrounding oxygen leaving aside defects, this means it has a 4+ oxidation state. But on very close inspection with x-ray spectroscopy its clear that the cerium hangs on to at least some of those four electrons and its true oxidation state is in a quantum mechanical limbo some where between 3 and 4.
 * I admit I haven't really kept a close eye on this article since I pushed it to GA in 2016; if you feel it should be sent to GAR, please feel free to do so. :) I see that most of the cn tags are for stuff about applications and biology; unfortunately the sources I have access to at the moment are mostly on chemistry, so I may not be able to fix them, but I can try looking. Double sharp (talk) 11:47, 24 January 2022 (UTC)
 * OK, I'll proceed. Jo-Jo Eumerus (talk) 16:37, 24 January 2022 (UTC)

Omission of use of cerium in grinding optics
The article appears to omit the widespread use of cerium oxide as a polishing agent for the manufacture of accurate lenses and mirrors. A suspension of cerium oxide particles is used instead of much harder silicon carbide or even harder diamond grains on the surface of a tool made with polishing pitch, especially in hand polishing, because you want a hardness closer to the softness of the glass surface being polished, to avoid the over-removal of glass from the surface being polished. David Spector (talk) 19:48, 12 November 2022 (UTC)

Source verification: Greenwood and Earnshaw (1997). Chemistry of the Elements (2nd ed.)
Does anyone have access to the Greenwood and Earnshaw ref? I would like to verify: The measured abundances of less common elements varies widely with the location tested. Consequently comparisons of "relative abundance" are often meaningless. Nevertheless wikipedia editors like to read the tables of abundance and draw their own conclusions.
 * "Cerium is the most abundant of all the lanthanides, "
 * "Thus, despite its position as one of the so-called rare-earth metals, cerium is actually not rare at all."
 * any comparison of abundance to the abundance of other elements similar to the one in the article.

Tnanks! Johnjbarton (talk) 15:55, 14 April 2024 (UTC)


 * Sure! According to G&E pg. 1229,
 * So, I guess it answers the second and third bullet points and indirectly the first (I guess?).  141 Pr  {contribs} 16:09, 14 April 2024 (UTC)
 * So, I guess it answers the second and third bullet points and indirectly the first (I guess?).  141 Pr  {contribs} 16:09, 14 April 2024 (UTC)