Wikipedia talk:WikiProject Elements/Archive 45

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"List of chemical elements" redesign

I am working on an overhaul of the table in List of chemical elements#List. If you are interested, please join the talk here. -DePiep (talk) 15:12, 29 March 2020 (UTC)

File:Mercury spectrum visible.png =? File:Barium spectrum visible.png

Hello,

An email we received on OTRS suggests that both pictures are identical.

Would someone be able to check if they are correct?

Best,

--AntonierCH (talk) 13:36, 5 April 2020 (UTC)

@AntonierCH: It indeed appears to be the case. Although the files differ in size by 20 bytes, I compared them via this tool and found no difference. I am not very experienced with this sort of stuff, but if I interpret the data from the National Institute of Science and Technology correctly, then this picture is likely not to be that of mercury, as the orange and red lines tell. And it's probably not barium either, because that would have a very strong green line in its spectrum at 554 nm. It sure beats me what this is. Perhaps if someone has more knowledge on this matter and can comment, that would be great, but for now, I am concerned about the whole set of spectra.--R8R (talk) 16:47, 5 April 2020 (UTC)
@R8R: I took a sample from another source - I have confirmed (at least 99.999% sure) that the image shows barium's spectrum. However, the intensities of the lines are a bit off. The bright green line (the last thick green line closest to yellow in the Wikipedia image) is a bit dim here. It could be a limitation of the software used to draw the lines. But the fainter lines are all showing up in exactly the correct places for barium. ― Дрейгорич / Dreigorich Talk 21:22, 5 April 2020 (UTC)
They are both cited to a Matlab function that is documented to come with table of spectral data. The README does not cite the sourse of the data. I cannot download the file to see the values or run it (to see if the results match the images) or if there is a cite somewhere internally.[1] Commons has about 100 spectra cited to that program[2] among the 160ish in commons:Category:Atomic spectra. DMacks (talk) 05:36, 6 April 2020 (UTC)
Did anyone ping User:McZusatz who uploaded the files? Long-inactive on commons but active on enwiki as recently as December. DMacks (talk) 05:38, 6 April 2020 (UTC)
@DMacks: I did on his Commons talk page, here. AntonierCH (talk) 13:46, 6 April 2020 (UTC)
Perfect thanks, and thanks also for starting c:Commons:Deletion requests/File:Mercury spectrum visible.png. I fixed the link to the user's notification in your message...stray slash char. DMacks (talk) 04:05, 10 April 2020 (UTC)

Isolation of an elusive phosphatetrahedrane

The first synthesis of a PC3 unit arranged in a tetrahedron, here.

This is quite something since plain all-carbon tetrahedrane (CH)4 has never been isolated. P was used in light of its capacity to form tetrahedral molecules, and the similarity of some of its properties to those of C, as noted in our nonmetal article, now updated. Sandbh (talk) 00:14, 14 April 2020 (UTC)

Careful...this was the tri-tert-butyl derivative of the C3P core, the same type of derivative of which the C4 core was made over 40 years ago (tetra-tert-butyl derivative). and it seems like the new molecule was made using an electronically equivalent final closure step as the second-generation synthesis of the all-carbon case. It's great to make unusual molecules (and especially to expand the scope of core atoms and the number of sterically shielding groups needed to be able to isolate it. But it's quite unlike what your "quite something since..." comment seems to imply. DMacks (talk) 05:25, 14 April 2020 (UTC)

@DMacks: Thank you for the feedback. Could you have a look at the nonmetal article, here, and let me know if my mention of this development is appropriate? It's in the "carbon and phosphorus paragraph", last two sentences. I tried to tone it down. See also this item in the Chemistry World weekly newsletter. Sandbh (talk) 08:10, 14 April 2020 (UTC)

Orbital radii and EN

Scatter plot of electronegativity and orbital radius of the chemical elements up to Lr, 103

Observations

  1. The results are similar to the orbital radii x EA chart, although not quite as clear, including being more crowded
  2. Very good correspondence with natural categories
  3. Largely linear trends seen along groups 1-2, 17 and 15-18 (Ne-Rn);
  4. First row anomaly seen for He (or maybe not since it lines up with the rest of group 2)
  5. For group 13, the whole group is anomalous
  2. For group 14 , the whole group is anomalous no doubt due to the scandide contraction impacting Ge and the double whammy of the lanthanide and 5d contraction impacting Pb
  3. F and O are the most corrosive of the corrosive nonmetals
  4. The rest of the corrosive nonmetals (Cl, Br and I) are nicely aligned with F
  5. The intermediate nonmetals (IM) occupy a trapezium
  6. Iodine almost falls into the IM trapezium
  2. The metalloids occupy a diamond, along with Hg; Po is just inside; At a little outside
  3. Rn is metallic enough to show cationic behaviour and falls into the metalloid diamond
  4. Pd is located among the nonmetals
  5. The proximity of H to Pd is again (coincidentally?) astonishing given the latter’s capacity to adsorb the former
  6. The post-transition metals occupy a narrow strip overlapping the base of the refractory metal parallelogram
  2. Curiously, Zn, Cd, and Hg (a bit stand-off-ish) are collocated with Be, and relatively distant from the PTM and the TM proper
  3. The ostensibly noble metals occupy an oval; curiously, W is found here; Ag is anomalous given its greater reactivity; Cu, as a coinage metal, is a little further away
  4. Au and Pt are nearest to the halogen line
  5. The ferromagnetic metals (Fe-Co-Ni) are colocated
  6. The refractory metals, Nb, Ta, Mo, W and Re are in a parallelogram, along with Cr and V; Tc is included here too
  2. Indium is the central element of the periodic table in terms of mean orbital radius and EN; Tc is next as per the EA chart
  3. The reversal of He compared to the rest of the NG reflects #24
  4. All of the Ln and An fall into an oval of basicity, bar Lr
  5. The reversal of the positions of Fr and Cs is consistent with Cs being the most electronegative metal
  6. A similar, weaker pattern is seen with Ba and Ra.
Yes, I definitely prefer this chart to the other one, even if I still think Pd is a warning sign that too much attention is being paid by orbital radii to the [Kr]4d105s0 configuration. Have you considered plotting single-bond covalent radii (doi:10.1002/chem.200800987) to remove this anomaly and deal with something indisputably chemical? As a bonus, it would probably let Rf through Og be plotted on the chart.
I'd generally agree with most of your points. While chemically speaking the 5d metals are not quite that electronegative, it's nevertheless true that overly high electronegativity values most scales assign them have some chemical meaning (strong homonuclear multiple bonding, maybe reflected in all those cluster compounds), so I won't quibble about that. Notice that Zr and Hf show up among the basic cations. ;)
I would rather say that the natural families mostly end before the 6p elements. There is a continuum near the edges (as usual); N, S, and Se can act as strong nonmetals when given the chance, and I is pretty weak for a nominally strong one. Double sharp (talk) 09:31, 2 May 2020 (UTC)

It's funny that you prefer this one to the EA chart. EA seems to get an undeserved bad rap where ever it goes, aside from the wisdom expressed by Myers…

"It is common in textbooks to see graphs showing ionization energy, IE, as a function of atomic number. One does not see such graphs for electron affinity, EA, even though this is necessary to understand the chemical hehavior of the elements. This may he because it is not realized how extensive the data are (13). The data are given in periodic table form in Figure 1, and graphed in Figure 2, which shows that, in general, EA has about the same periodic hehavior as does IE. There are some deviations from strict periodicity, most of them having interesting and instructive explanations. Some of the divergences from periodic hehavior are unexplained."

…and Wulfsberg (2018), as posted by me a little while ago; and that in general, the higher an element's ionisation energy, electron affinity, and electronegativity, the more nonmetallic that element is (Yoder CH, Suydam FH & Snavely FA 1975, Chemistry, 2nd ed, Harcourt Brace Jovanovich, New York, p. 58).

@Sandbh: Of course it deserves the bad rap. You can't apply it consistently to all elements, because many of them simply don't form bound negative ions. Double sharp (talk) 04:56, 6 May 2020 (UTC)

The next chart I was going to look at was OR x IE. I hadn't thought about single-bond covalent radii, but will have a look at that one too. Yep, agree about continua. It's the line about the distinction between categories not being absolute; boundary overlaps occur as outlying elements in each category show or begin to show less-distinct, hybrid-like, or atypical properties. I is good, not forgetting its capacity to dissolve gold. Sandbh (talk) 03:38, 6 May 2020 (UTC)

@Sandbh: Don't forget that sulfur attacks silver (and that sulfur has comparable electronegativity to iodine). And selenium and tellurium have strong chemical affinity towards Ag and Au. So just looking at one element alone is not going to be a good holistic measure for whether a given nonmetal is strong or not. You'd do better looking at how good those nonmetals are as oxidising or reducing agents: stronger nonmetals make better oxidising and worse reducing agents. Nitrogen and sulfur are then fair game as strong nonmetals, looking at it that way. (Selenium can maybe be argued about, I suppose.) Double sharp (talk) 04:27, 6 May 2020 (UTC)

White lead

Hi, I'd like to learn what "white lead" is. According to Catholic Encyclopaedia, in the antiquity there was a metal named white lead which was used to mint coins. The source says it was Molybdenum. But for some reason I find it quite improbable. Can it be chromium or another element ? Thanks. Nedim Ardoğa (talk) 07:01, 10 May 2020 (UTC)

@Nedim Ardoğa: maybe it was plumbum album. According to this (and our article, referring to plumbum candidum) it was tin, but this seems to suggest it was a silver-containing alloy. I suspect from what I read here that it was an alloy containing at least Pb, Sn, and Ag, but I don't know enough to be sure. Cr and Mo indeed seem quite unlikely, although I cannot rule out that perhaps they were sometimes also included accidentally without knowledge of their presence or what they were. Double sharp (talk) 07:09, 10 May 2020 (UTC)

@Nedim Ardoğa: The CE entry says:

"Zephyrium, a titular see in Cilicia Prima, of Tar-sus. Nothing is known of the history of Zephyrium, lying on the coast of Cilicia, between Cilicia Tracheia and Pedias. This city is mentioned, however, by numerous ancient authors—it had many coins; here was prepared the best molybdenum (white lead), drawn from the neighboring mines of Corcyra.”

Pliny says:

”The next topic is the nature of lead, of which there are two kinds, black and white. White lead {tin} is the most valuable; the Greeks applied to it the name cassiteros, and there was a legendary story of their going to islands of the Atlantic ocean to fetch it and importing it in platted vessels made of osiers and covered with stitched hides.”
“…and white lead yields no silver, although it is obtained from black lead.”
"There is also molybdaeaa (which in another place we have called galena); it is a mineral compound of silver and lead. It is better the more golden its colour and the less leaden: it is friable and of moderate weight. When boiled with oil it acquires the colour of liver. It is also found adhering to furnaces in which gold and silver are smelted; in this case it is called metallic sulphide of lead. The kind most highly esteemed is produced at Zephyrium."

Someone has their colours the wrong way round.

I guess white lead was galena, or PbS, with a 7.2–7.6 specific gravity. It’s the most important ore of lead and an important source of silver. In some deposits the galena contains about 1–2% silver, a byproduct that far outweighs the main lead ore in value. In these deposits significant amounts of silver occur as included silver sulfide mineral phases or as limited silver in solid solution within the galena structure. These argentiferous galenas have long been an important ore of silver.

I guess black lead then was cassiterite, SnO2, with a 6.98–7.1 specific gravity. Sandbh (talk) 12:50, 13 May 2020 (UTC)

β- (left) and α-Sn; the former is the stable form at room temperature
Pb. Note the darker colour, compared to β-Sn.
@Nedim Ardoğa: In fact, it is plumbum candidum / plumbum album (bright lead / white lead) that was Sn; plumbum nigrum (dark lead) was Pb. Anyone can see that metallic Pb is darker than β-Sn; this and its high density gave it superstitious chthonic connexions (Forbes, below). It's fairly obvious from the name cassiteros Pliny mentions for white lead that this ought to be related to cassiterite (SnO2), which Sandbh guesses is black lead, at variance with the identification made by reliable sources.
Let me quote R. J. Forbes' Studies in Ancient Technology, Volume VIII (first published 1964), p. 204:


Incidentally, this series would probably make an excellent source for those wanting to FA our ancient-metals articles. ^_^
Only this way round does the statement Sandbh quotes Pliny as saying make sense ("white lead yields no silver, although it is obtained from black lead"), because Ag occurs often with Pb ores, but not Sn. To quote Silver#Occurrence and production:
It is true that the white lead used to mint coins was a mixture containing Ag and Pb as well, judging by this source. And many artefacts from the Roman period mix Sn and Pb (judging from that source), which is not surprising if you consider the "confusion" that Forbes remarks. But it surely seems that when the qualifiers were added (implying that the distinction was important for some reason), there is no doubt that black lead must have referred to Pb, not Sn. Double sharp (talk) 14:12, 13 May 2020 (UTC)
Cassiterite
Galena with baryte and pyrite

The situation isn't clear, and the sources are confusing.

I had in mind the black appearance of cassiterite (SnO)—which I've seen referred to as black tin ore and white tin ore—and the shiny appearance of argentiferous galena (PbS). If coins were being made from molybdaeaa (galena) I guessed this was done using the silver content, rather than the lead content.

I've never heard of Roman coins made of Pb, nor Sn coins for that matter.

Stibnite, plumbum cinereum

And why would plumbum cinereum (antimony) be called that apart from the grey appearance of stibnite?

Here's Pliny again:

"The substance of white lead has more dryness, whereas that of black lead is entirely moist. Consequently white lead cannot be used for anything without an admixture of another metal, nor can it be employed for soldering silver, because the silver melts before the white lead."

How can the silver melt (961.78 °C) before the white lead? The MP of galena is 1,114 °C. That of cassiterite is 1,630. The MP of tin is 231; that of Pb is 327.

In this article doi:10.1111/j.1468-0092.1984.tb00124.x the author says:

"Plumbum nigrum, 'black lead', was true lead. Plumbum candidum or plumbum album, ‘white lead’, was tin. Pliny uses both terms apparently interchangeably in the same chapter (book 34, chapter XLVII)." For example, he writes, "White lead is naturally more dry; while the black, on the contrary, is always moist; consequently the white, without being mixed with another metal, is of no use." We know in fact that the addition of tin improves wetting properties of an alloy; lead itself has poor wetting characteristics.

This is from Metallographia (17th C):

"It is not amiss here to give the differences betwixt white Lead, or Tin, Bismuth, Tin-glass, or ash-co∣loured Lead, and this common Lead, which they call black Lead; according as Agricola hath set them down:* who saith; The white Lead or Tin, before it be polished, doth shine much; but polished, much more; the ash-coloured much less, the black not at all. The white is more perfect and precious then the black, the ash-coloured holds the mean betwixt them. The black is most easily melted, and doth not long indure."

Now the MP of Pb is 327 C and of Sn is 231. So here, tin seemingly = black lead.

Cerussite

And there is cerussite (from the Latin cerussa, white lead) or PbCO3, an important ore of lead, which I've seen referred to as white lead ore or black lead ore.

The source quoted by Double sharp refers to "a single industrial process involving the reduction and refining of argentiferrous [silver bearing] white lead/black tin."

It also says,

"…most silver was obtained by the cupelation of "fertile" or argentiferous lead, the silver being separated from the litharge produced in refining and left unaltered. The residual litharge was then resmelted to produce "sterile" or de- silvered lead which formed the major European supply of that metal. Yet such deposits were not alone in yielding the precious white metal. Argentiferous coppers subject to oxidation could be made to release silver which, taken up to into lead, could be extracted by the cupelation process described above. Then again there was a curious geological formation yielding ores which on first smelting produced an argentiferous lead-tin compound, a kind of natural pewter, which passed in contemporary parlance by the names plumbum album (white lead) or stagnum nigrum (black tin). Subsequent smelting separated the constituent elements. The silver bearing lead, being subjected to the process described above, produced "sterile" lead and silver, providing a supplementary supply of these metals to that of the silver-lead industry. The white tin, known simply as stagnum purged of plumbiferous impurities formed the principal European supply of that metal." (p. 3)^

^ On the nature of these workings, see: Blanchard, Stagnum or Plumbum Album: Post-Roman British Metal Production and International Monetary systems. ca. 420-620 AD (The University of Edinburgh: Studies in Economic Social History, Discussion Paper No.3. 1993).

Litharge, a secondary mineral which forms from the oxidation of galena ores

So perhaps the "white lead" being used in Zephyrium was this argentiferous lead-tin compound-mixture, with the silver being used for coinage. Sn was needed to make bronze, especially weapons and armour. There is this paper doi:10.1007/s11837-010-0118-3 which refers to, "…evidence related to the genesis and occurrence of mixed lead-tin ore deposit consisting of cassiterite and the secondary minerals formed from galena. These evidences belong to a very long time period ranging from pre-historic to as late as the nineteenth century A.D. This type of mixed ore deposits was smelted to prepare lead-tin alloys." The ores involved appear to have been cassiterite, and cerussite a weathering product of galena.

From here, we have:

"This was probably lead ore in its primary state, when only separated from the stannum,^ and before it was subjected to fusion for the purpose of obtaining pure lead.—See Beckmann's Hist. Inv. Vol. II. p. 211. Bohn's Edition. Ajasson identifies it with litharge, or fused oxide of lead, known as gold and silver litharge, from its colour."
^ A compound metal, probably, somewhat like pewter. 

--- Sandbh (talk) 08:10, 14 May 2020 (UTC)

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