Talk:Noble metal

Suggestion to rename to "Noble metals" (plural form)
In line with quite a number of other wikipedia articles (Refractory metals, Coinage metals, Heavy metals, Native metals), and since this page describe a group of several metals called "noble metals", it would make sense to rename this article into "Noble metals". Ileresolu (talk) 07:48, 11 May 2021 (UTC)

Same proposal for Precious metal.Ileresolu (talk) 08:40, 11 May 2021 (UTC)
 * This question came up in some others, where I find the singular more obvious. In chemistry, often enough one wants a generic halide for example, so not in the group sense. I note, though, that this one wasn't recently renamed. In any case, I am less sure it should be singular, than for some others. Gah4 (talk) 22:37, 9 February 2022 (UTC)
 * This question came up in some others, where I find the singular more obvious. In chemistry, often enough one wants a generic halide for example, so not in the group sense. I note, though, that this one wasn't recently renamed. In any case, I am less sure it should be singular, than for some others. Gah4 (talk) 22:37, 9 February 2022 (UTC)

Clean up errors in Periodic Table illustration
Cobalt is misspelled "Coblat". Silicon appears twice as #14 and #16. Sulfur is missing.

I simply deleted this illustration. In addition the errors listed above, the Wells reference cited does not have a page 885. I think they meant 385. The bigger problem with the illustration, however, is that it misinterprets the Zaki reference. Zaki is not listing noble metals as a group, but is explaining nobility in the electrochemical sense. i.e. In relationship the the hydrogen reduction potential. Therefore, it confuses the group and the property as outlined in the article. I will try to clean that up.

The illustration was nice and, if it can be re-done with these corrections, I think it would be helpful. I think it is better left out than remain with these errors however. A15730 (talk) 18:35, 28 March 2022 (UTC)


 * , thanks for your diligence. That's good to see.


 * Posts to talk pages go at the end of the page, not at the start, so that chronological order is preserved.


 * I fixed the errors in the image, and have updated Wells. I don't know who Zaki is. No Zaki is mentioned in the article.


 * I reverted your other edit as it disrupted the existing structure of the article, ignored the image, and had unsupported content.


 * Re your deletion of "most often" from "The set of noble metals most often consists of..." there is no standard widely agreed and defined set of noble metals in the literature. So, "most often" is probably the best that can be currently done.


 * I have an interest in noble metals and am happy to help you and discuss the article, proposed changes, and my reversions of your edits.


 * thank you, Sandbh (talk) 07:18, 29 March 2022 (UTC)
 * If by Zaki you mean Ahmad Z, then this author writes, "Cu, Ag, Au are examples of noble metals..." and "Metals with large positive potentials are called 'noble' metals because they do not dissolve easily. Examples are copper, silver, gold, etc." The fact that Ahmad is explaining nobility in the electrochemical sense does not therefore mean that silver and gold are not noble metals.


 * The fact that noble metals have large positive potentials, as discussed in the Electrochemical section, is one of the reasons why they are referred to as noble metals. Sandbh (talk) 07:29, 29 March 2022 (UTC)
 * Thank you for working on that table. I am new to this and could not get it done.  Anyways, elements 14 and 16 still both show "Si" as the element.
 * With regards to the Zaki Ahmed reference, yes, I was referring to the reference in the table to color copper. Thank you for making that connection.  I agree that the fact that Ahmed is explaining nobility in the electrochemical sense does not mean that silver and gold are not noble metals, but the fact that they meet the property of electrochemical nobility relative to hydrogen does not mean that they ARE noble metals.  i.e.  The Ahmed reference supports the statement that "noble" can be used as an adjective as explained in the article section on meaning.  It does not name the metals relative to its use as a noun or otherwise give a listing.
 * With regards to the structure and "unsupported content", I am not sure what you mean.  Sorry.  What I was attempting to do was to give information which would allow reconciliation with the fact that most current listings of noble metals (and all which I have seen) do not include copper, rhenium, and mercury.  I think this is done easily by pointing out the distinction between adjective and noun which is already given in the article but was not always clear.
 * The main point here is the deletion of the words "most often". I cited two standard English language references which give the list.  Neither notes there is any other listing.  I checked the other current, standard, references available to me (in electrochemical and material sciences).  I did not find any list with copper, rhenium, or mercury or mention that they may be noble metals.  So, where does this come from?  I see that the reference for the list appears to be a German language reference book.  I do not read German and do not have access.  So, I cannot verify if it gives a list or gives a statement regarding variance with lists.  The statement that "More inclusive lists include one or more of copper (Cu), rhenium (Re), and mercury (Hg) as noble metals." has no reference.  Is the reference for this also the German text?
 * I looked quite hard and could not find mention of these extra elements in any currently used textbook. This is, of course, only what I have access to.  Have you found a list in any standard reference book today which contains copper, rhenium, and mercury?  If not, I think it is a historical appendage best put under the "meaning and history" section for clarity and readability.  I also believe it would be accurate as I am sure that at one time there was more variation due to conflation of the uses of the word "noble", I just don't think that is true to any significant degree today... I realized that the Tamboli reference given in the table which list rhenium as a noble metal, though not a standard reference, would be a counter example as it was published in 2010.  Reading this paper, however, I can find no mention of rhenium.  (It does, however, seem to suggest that the authors do not consider copper to be a noble metal with the wording, "Ruthenium is a noble metal and does not oxidize readily. Hence, it is possible to directly plate copper on ruthenium."  Their rationale is flawed, but I think that would be an illogical statement to make if they also though copper was a noble metal.)  Anyways, please review and amend that in the table as well, if you see fit. A15730 (talk) 15:04, 29 March 2022 (UTC)

Good to hear from you. We all started as newbies and it'll get easier.

I fixed the symbol for sulfur.

Since WP is an encyclopaedia we can, to a large extent, only base our articles on what other reliable sources say. On noble metals, there is no widely agreed list of these in the literature. The best we can do is to indicate which metals are commonly referred to as such, supported by some sources. Then, in the interests of comprehensiveness, note the outliers, such as copper, rhenium, and mercury. That is what the article currently tries to do. Other sources mention copper as a noble metal given, as I understand it, its membership of the group 11 coinage metals. Mercury has a long history of a special status, dating back to at least alchemical days, given its shiny appearance, liquid status, and relative non-reactivity.

If by "reference for the list" you mean A. Holleman, N. Wiberg, "Inorganic Chemistry", Academic Press, 2001, that is a German text translated into English, and widely regard as one of the big three alongside Cotton & Wilkinson, and Greenwood & Earnshaw. Wiberg says, "In contrast to the reactive alkali metals... the coinage metals are noble (unreactive)." (p. 1248) Wiberg does not otherwise say which elements are noble metals. He does say, "In place of the noble gases, the transition metal grouping has the noble metals." (p. 1133).

The statement that "More inclusive lists include one or more of copper (Cu), rhenium (Re), and mercury (Hg) as noble metals" may be dubious, and there may not be any such more inclusive list in the literature. It could be better worded or deleted.

I have corrected the source for Re, thank you. More to follow. Sandbh (talk) 07:20, 30 March 2022 (UTC)


 * Thank you for taking the time to read through this and trying to understand what I am saying. Even though I can see you are experienced doing this and have some passion for it, I'm sure it still takes considerable time.  Hopefully, I can make clear to you the change I think needs to be made with the following explanation:
 * Of the books I have before me, which actually do include both Cotton and Wilkinson, and Greenwood and Earnshaw, I have only two which I find which explicitly say "The noble metals are...". The first is "Corrosion Engineering" by Fontana which is a highly respected book and gives the list:  gold, silver, platinum, iridium, osmium, palladium, rhodium, and ruthenium.  The other is the college level textbook, "Material Science and Engineering" by Callister which gives the list:  silver, gold, platinum, palladium, rhodium, ruthenium, iridium, and osmium.  Checking other books on-line, I find "The Analytical Chemistry of Noble Metals" by Beamish, as well as other texts by him, which give the list:  Ruthenium, Osmium, Rhodium, Iridium, Palladium, Platinum, and Gold.
 * This falls in line with the knowledge of my colleagues, who I polled, and myself who have generally the same understanding from our experience, education, papers, etc. i.e.  General perception of current reality.  We would generally include rhenium and possibly not include silver, with mercury being included but more of as the answer to a trivia question, but don't consider these to be significant disagreements.  So, I agree with most everything you have written.
 * My problem is with the inclusion and placement of the statement that "More inclusive lists include one or more of copper (Cu), rhenium (Re), and mercury (Hg) as noble metals" and associated wording which give the impression that if one were to get any respected text or ask a scientist or an engineer in an associated field to find out what the noble metals are, that there is some significant chance, say 1 in 3 or 1 in 4, that copper would be included. So, I ask where is this list?  The lists that I can find seem to agree that copper is not included.  As far as Zaki Ahmed, I repeat that he is not giving a list.  If you think that that is a list, then you must think that he is limiting the noble metals to just gold, silver, and copper.  If you think he is not limiting them to gold, silver, and copper, then you understand that he is giving the electrochemical criteria of nobility with respect to hydrogen-- I am very familiar with this field and use the wording the same way.  i.e.  This is not a contradiction.
 * Regarding the Wiberg reference, thank you for the explanation. I do not have it before me but was able to access an English translation via google.  It is supposedly the 2001 print with 1884 pages.  It also uses the word "noble" as a flexible adjective when relating one element to other.  (See for instance, the discussion of titanium where it says that it is noble to one metal but not another.)  I believe this is what is intended in the segment you quote on page 1248.  I realize that, at first glance, that may seem like a stretch, HOWEVER, WIBERG MAY GIVE AN UNAMBIGUOUS LISTING OF NOBLE METALS.  See at the bottom of p. 1458, "Of 8 the noble metals (6 platinum metals + Ag + Au), silver is the most abundant."  Looking at the listings on page 1458 and 1487 clearly establishes the 6 platinum metals per Wiberg as platinum, palladium, iridium, rhodium, osmium, and ruthenium.  (I believe this is meant to read, "Of the 8 noble metals..."  Please check the original if you are able.)
 * So, again, where does copper come from? I could only find instances where "noble" was being used as a property.  The Wiberg reference is actually much closer than anything I have seen in declaring it a group member, but I note that it is a translation and it appears to contradict that interpretation on the same page.  I still have not seen a single listing intended to be comprehensive stating "The noble metals are..." with copper following.  As far as the statement, "More inclusive lists include one or more of copper (Cu), rhenium (Re), and mercury (Hg) as noble metals", you may ask why I didn't just delete this along with the associated wording?  The answer is because I believe that this MAY have been true at some point in the past.  By that, I mean the 1800's when chemistry was more of an open field.  In fact, I suspect that that line actually comes from an old Encyclopedia Britannica entry.  My point is that it does not seem to be true today, however, and it is misleading to make it appear so.  That is why I moved it to the "history and meaning" section along with the citation from the early 1900's stating explicitly that copper was not a noble metal.  i.e.  I was trying to preserve the information without giving a misleading impression of the current reality which is simply that the noble metals do seem agreed to be the platinum group metals plus gold, with silver, rhenium, and mercury also being included by significant groups.  Best Regards. A15730 (talk) 16:33, 30 March 2022 (UTC)


 * Britannica (the modern one) lists Re with H&W's list of 8. It still says that Cu and Hg are "sometimes included". But it does seem weird to me to include Cu today, because it reacts with moist air.
 * An electrochemical criterion wrt hydrogen would imply that Bi is a noble metal, which seems like a novelty. Double sharp (talk) 02:30, 31 March 2022 (UTC)

Extracts from the literature
,, thanks; here are some extracts from the literature:
 * 1) The Chemistry Leaflet 1936, vol. 10, p. 3
 * "The atomic structures of these metals are discussed in the paragraphs which are given below. Copper, not ordinarily classed as a noble metal because it is found more commonly in nature than the others mentioned, is included in the following discussion because its atomic structure is quite similar to that of gold."
 * 1) Elements of Chemistry, Brownlee et al. 1943, p. 504
 * "The noble metals, copper, silver, and gold, were the first used by man and were called noble because they withstood heat and corrosion."
 * 1) Mechanical World and Engineering Record 1946, vol. 119, p. 6
 * "It [bismuth] is also a comparatively noble metal…"
 * 1) The Extraction of Non-ferrous Metals 1950, Roberts ER, p. 118
 * "Bismuth is relatively noble, and can be liberated from the native alloys by the simple process of liquation without any undue oxidation occurring."
 * 1) Mellor's Modern Inorganic Chemistry 1952, Parkes GD, p. 636
 * "Gold is not acted upon by air or oxygen at any temperature, hence the alchemists called gold a noble metal on contrast with base metals—like copper, lead, tin, etc.—which are oxidized and lose their metallic character when heated in air. Silver and platinum are also noble metals."
 * 1) Treatise on Inorganic Chemistry: Sub-groups of the periodic table 1956, Remy H & Kleinberg J, p. 361
 * "…among the most active of the elements, the metals of the first Sub-group are noble metals. The alkali metals stand at the top, copper, silver and gold at the bottom, of the electrochemical potential series."
 * 1) Using Chemistry 1959, Lanford OE, p. 604
 * "Because of their low degree of chemical activity, copper, silver, and gold are known as noble metals"
 * 1) Metals Engineering Quarterly, vol 1, 1961, p. 110
 * "Rhenium occupies a position in the third long period in group VIII B of the periodic chart of the elements, which is the most refractory position of group VII, midway between highly refractory metals such as tantalum and tungsten, and noble metals such osmium, iridium and platinum. This unique position suggests a combination of refractory metal and of noble-metal properties."
 * 1) Theory of Corrosion and Protection of Metals: The Science of Corrosion 1966, Tomashov et al., p. 648
 * "Silver, rhodium, copper, and mercury have standard potentials less positive than +0.81 V. Consequently these metals will not dissolve by hydrogen depolarization (in nonoxidizing acids), but they can corrode by oxygen depolarization—that is, in aqueous corrosion media in the presence of oxygen These metals can be termed seminoble metals . Nevertheless we traditionally consider silver as a noble metal."
 * 1) A Dictionary of Mining, Mineral, and Related Terms 1968, Bureau of Mines, p. 753
 * "noble metal(s). a. A metal whose potential is highly relative to the hydrogen electrode. ASM Gloss. b. A metal with marked resistance to chemical reaction, particularly to oxidation and to solution by inorganic acids. The term is often used synonymously with precious metal. ASM Gloss. c. The metals which have so little affinity for oxygen, that is, are so highly electronegative, that their oxides are reduced by the mere application of heat without a reagent; in other words, the metals least liable to oxidation under ordinary conditions. The list includes gold, silver, mercury, and the platinum group (including palladium, iridium, rhodium. ruthenium. and osmium). The term is of alchemistic origin."
 * 1) "The corrosion and electrochemical behaviour of rhenium", 1968, Tomashov ND & Matveeva TV, in Corrosion and Protection of Structural Alloys, Part 1, Mercer AD (ed.), p. 189
 * "Thus, in acid solutions rhenium behaves as an electropositive metal. In terms of thermodynamic stability rhenium occupies ninth place after gold, platinum, iridium, palladium, rhodium, silver, mercury, copper. It can be classified with those metals which have an intermediate thermodynamic stability (semi-noble metals). These include rhodium, silver, mercury, copper, rhenium, bismuth and antimony and the group is characterised by the fact that these metals are thermodynamically stable in acid and neutral solutions only in the absence of oxygen or oxidizing agents."
 * 1) Chemistry for Technologists 1972, Palin GR, p. 158
 * "Few elements occur in nature in the uncombined state…A few of the so-called noble metals are found in the elemental form. These include copper, mercury, platinum, silver and gold, although much of the copper, mercury and silver which occurs is found in the combined state."
 * 1) The Metallic Elements 1977, Parish RV, p. 112
 * "The metals of Group VIII (Ru, Os, Rh, Ir, Pd, Pt) are often grouped together as the platinum group metals and they, together with silver and gold, are often known as the noble metals on account of their chemical inertness (in the elemental state)."
 * 1) CRC Handbook of Lubrication: Theory and Practice of Tribology Volume II, 1983, Bruce RW (ed)
 * "The metal surface has an effect. Copper, silver. and gold are noble metals and many of their properties are similar. Yet, oxygen will chemisorb relatively strongly to copper. weakly to silver, and not at all to gold. Reactivity of the adsorbent is also important. Of the halogen family ﬂuorine will adsorb more strongly than chlorine. chlorine than bromine. and bromine than iodine."
 * 1) Noble Metal Alloys 1986, TMS Thermodynamics Committee, p. v
 * "Research on the alloying behavior of the noble metals copper, silver and gold has always been of prime importance in the theory of alloys."
 * 1) Experimental Inorganic/Physical Chemistry 1999, Malati MA, p. 219
 * "Together with Cu and Au and some heavier transition metals, they [inc. Ag] are described as noble metals."
 * 1) Introduction to Modern Inorganic Chemistry 2002, 6th edition, Mackay RA & Henderson W, p. 43
 * "Noble metals: An ill-defined term applied to the platinum metals, Au, and sometimes includes Ag, Re, and even Hg."
 * 1) Corrosion of Linings & Coatings: Cathodic and Inhibitor Protection and Corrosion Monitoring 2006, 2nd ed., Schweitzer PA pp. 422—423
 * "Noble coating metals that provide corrosion protection by means of EMF control include copper, silver, platinum, gold, and their alloys. The standard single potentials of these metals are more noble than those of hydrogen…Therefore, the oxidizer in corrosion cells formed on these metals in a natural environment, containing no other particular oxidizers, is dissolved oxygen. Consequently, the electromotive force that causes corrosion is so small that coating with noble metals is an effective means of providing corrosion protection. With the exception of copper, the other members of this group are precious metal and are primarily used for electrical conduction and decorative appearance."
 * 1) Metals and Chemical Change 2007, Johnson D (ed.), p. 27
 * "The so-called noble metals... are often found free or can be obtained by heating their ores in air. This... class includes gold, silver, mercury... More easily oxidized metals, which are often obtained by heating their ores in air to form oxides, then heating the oxides with some form of carbon at furnace temperatures up to about 1 500 °C, and then cooling... This second class includes copper..."
 * 1) Nanomaterials Chemistry: Recent Developments and New Directions 2007 Rao et al., p. 4
 * "This method has been extremely successful in yielding noble and near-noble metals such as Au, Ag and Pt."
 * 1) Basic Concepts of Chemistry 2008, Malone & Dolter, p. 111
 * "Classifying the elements doesn’t stop with. the division of elements into metals and metals. Further classification is possible because some elements have remarkable chemical similarities to each other. For example, several important metals are found in the free state in nature because of their low chemical reactivity. Copper, silver, and gold are metals that are very resistant to the chemical reactions of corrosion and rust. Because of this as well as their luster and, beauty, they are the prized metals of coins and jewelry. Gold and silver coins on the ocean bottom. deposited from ships that foundered hundreds of years ago, can be easily polished to their original luster.
 * Historically, elements with similar or related properties were grouped into what was referred to as families of elements. Thus, copper, silver, and gold were classiﬁed. as one family, sometimes referred to as the noble metals, while lithium, sodium, and potassium were classiﬁed into another family sometimes referred to as the active metals."
 * 1) Positrons in Solids 2012, Hautojärvi P, p. 66
 * "The noble metals include copper of which the band structure and Fermi surface are accurately known by other methods."
 * 1) Chemical Principles of Textile Conservation 2012, Timar-Balazsy A & Eastop D, p. 134
 * "The metals most commonly used to manufacture metal threads, gold, silver and copper, belong to the 'noble metals'."
 * 1) Applications of Environmental Aquatic Chemistry: A Practical Guide 2012, 3rd ed., Weiner ER. p. 262
 * "Metals that are resistant to oxidation and corrosion under common environmental conditions are sometimes referred to as noble metals. In addition to gold, silver, and platinum, they may include copper, mercury, aluminum, palladium. rhodium, iridium, tantalum, and osmium."
 * 1) Trace Elements in Igneous Petrology: A Volume in Memory of Paul W. Gast 2013, Allègre CJ & Hart SR, p. 102
 * "Refractory siderophile elements Ir and Re, together with a number of other noble metals (W, Os, Ru, Pt) are among the first elements to condense out of gas of solar composition…"
 * 1) Introduction to Chemistry 2013, Turk A, p. 466
 * "Metals that meet the requirement of being resistant to oxidation include bismuth, copper, mercury, silver, gold, and the platinum group."
 * 1) Chemistry 2013, Whitten et al. p. 1032
 * "Noble metals, such as Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au, can be found in the uncombined free state as the native ore."
 * 1) Heterogeneous Catalytic Materials: Solid State Chemistry, Surface Chemistry and Catalytic Behaviour 2014, Busca G, p. 301
 * "On the other hand. during oxidation reactions… the atmosphere is oxidizing, and thus only very few metals [the so-called noble metals, i.e. platinum group and group 1B (or group ll) metals i.e. copper, silver and gold] may stay (but not always are entirely) in the metallic state…"
 * 1) Dictionary of Environmental Engineering and Wastewater Treatment 2016, Bahadori & Smith, p. 289
 * "Noble Metal A metal which is not very reactive (as silver, gold, or copper) and may be found naturally in metallic form on earth."
 * 1) Chemistry 2016, Zumdahl SS, Zumdahl SA & DeCoste DJ, p. 726
 * "Some metals, such as copper, gold, silver, and platinum, are relatively difficult to oxidize. These are often called noble metals."
 * 1) Thermodynamics of materials corrosion 2018, Huang Y in Materials Corrosion and Protection, Huang Y & Zhang J (eds.)(eds), pp. 25–57 (31—32)
 * "2.2.4 Metal's thermodynamic stability in aqueous solution
 * Metal corrosion mostly occurs in aqueous solutions. The thermodynamic stability of the metal in an aqueous solution can be determined approximately by using the datum of standard electrode potential. According to the equilibrium potentials of hydrogen electrode at pH = 7 (neutral solution) and pH = O (acidic solution) being —0.414 V and 0 V, respectively, and the equilibrium potential of the oxygen electrode being +0.815 V and +1.23 V, respectively, all metals are classiﬁed into ﬁve groups with different thermodynamic stabilities.
 * Group I: quite thermodynamically unstable metal (active metal): E° < —0.414 V
 * The standard electrode potential of metal is less than the equilibrium potential of the hydrogen electrode, i.e., < —0.414 V. In a neutral aqueous solution, the metal can corrode in conditions without oxygen and oxidizing agent. The representative metals include Mg, Zn, Fe, etc.
 * Group 2: thermodynamically unstable metals (second active metal): —0.414 V < E° < 0 V
 * The standard electrode potential of the metal is higher than the hydrogen electrode equilibrium potential in a neutral solution but less than the hydrogen electrode equilibrium potential in an acidic solution. Without oxygen, the metal is stable in neutral medium, while in the acidic solution, metal can be corroded. Representative metals include Cd, Ni, Pb, etc.
 * Group 3: moderately thermodynamically stable metals (seminoble metals): 0 V < E° < 0.815 V
 * The standard electrode potential of the metal is higher than the hydrogen electrode equilibrium potential in an acidic solution but less than the oxygen electrode equilibrium potential in a neutral solution. In the absence of oxygen, both metal in a neutral medium and metal in an acidic medium are stable. The representative metals include Sn, Cu, Ag, etc.
 * Group 4: highly thermodynamically stable metals (noble metal): 0.815 V < E° < 1.23 V
 * The standard electrode potential of the metal is higher than the oxygen electrode equilibrium potential in a neutral solution but less than the oxygen electrode equilibrium potential in an acidic solution. In neutral solution containing oxygen, the metal does not corrode but may corrode in an acidic solution containing oxygen and oxidant. The representative metals are Pd, Ir, etc.
 * Group 5: completely thermodynamically stable metal: E° > 1.23V
 * In all metals, Au is the most resistant to corrosion and does not corrode even in an acid solution with oxygen. However, Au can dissolve into the complexing agents with an existing oxidant, such as 2Au + 4KCN + ½O2 + H2O —> KAu(CN)2 + 2KOH. The variation of the Gibbs free energy for the reaction is negative, AG° = —45KJ.
 * As it can be seen from the above discussions, under the natural conditions, only a handful of metals, such as noble metals in groups 4 and 5, can be considered completely stable. In neutral aqueous solutions, even without the presence of dissolved oxygen, the vast majority of metals are thermodynamically unstable, with a tendency to corrode spontaneously. It should also be noted that thermodynamic stability depends not only on the nature of a metal but also the corrosive agent. Thermodynamically stable metals (group 4) may corrode in the acidic solution containing oxygen and strong oxidant. Even the completely thermodynamically stable metal Au may become a thermodynamically unstable metal in an oxidizing solution containing complexing agents as its electrode potential becomes negative. In contrast, in the liquid saturated hydrocarbon without moisture and oxygen, the most active metals become completely stable."
 * 1) Emerging Applications of Nanoparticles and Architectural Nanostructures: Current Prospects and Future Trends 2018, Makhlouf ASH & Barhoum MA, p. 430
 * "Amongst the noble metals, copper is definitely the most reactive and toxic one. Copper is approximately six times cheaper than silver and 24 times cheaper than gold. and Cu nanoparticles exhibit efficient biocidal properties. Some reports have demonstrated that copper nanoparticles can show even greater antibacterial effects than silver nanoparticles. These biocidal properties and other available application areas such as catalysis, anti-fouling. anti-microbial. and energy applications have made scientists investigate for ways to reduce copper nanoparticle toxicity and make them safer to implement in those areas. Copper nanoparticles are already used in wound dressing and clothing.
 * Although known to possess efficient antimicrobial properties copper metal nanoparticles are very sensitive to oxygen and are easily oxidized under air. which decreases their efficiency against bacteria. In addition. this sensitivity to oxygen makes them pyrophoric and dangerous to handle under air. Plant mediated synthesis of copper nanoparticles can offer protection against oxidation as well as toxicity against human cells. when nontoxic capping is provided by biomolecules from plant extracts. Therefore biosynthesized copper nanoparticles have great potential for medical applications and coatings and sometimes can possess better anti-bacterial properties compared to conventional copper nanoparticles."
 * 1) "Organizing the transition metals", 2018, Rayner-Canham G in Scerri E & Restrepo G (eds), From Mendeleev to Oganesson, p. 205
 * "This author would contend that silver is so much more chemically-reactive and has such a different chemistry that it should not be considered as a "noble metal."
 * 1) History of Nanotechnology: From Prehistoric to Modern Times 2019,  Sharon M (ed.)
 * "However, the noble metals, such as Ag, Au, and Cu (coinage metals), are quite exceptional, as they form air stable colloids and exhibit fascinating optical properties due to excitation of the surface plasmon resonances in the visible regime of the EM spectrum…"
 * 1) Physical Properties of Materials for Engineers 2020, Pollock DD, p. 39
 * "Hume-Rothery and others have shown that many of the constitution diagrams of the noble metals (copper, silver, and gold) with metals belonging to the B subgroups show very similar phase relationships and structures. The copper-zinc constitution diagram is typical of these."
 * 1) The Chemistry of Money 2020, Rohrig B
 * "Copper: The Humblest of the Noble Metals."
 * 1) The Elements: A Visual History of Their Discovery 2021, Ball P, p. 36
 * "But this resistance to corrosion is rather unusual among metals, and it is why the coinage metals are the original members of a family known by the medieval name of the noble metals."

Comments
A15730, I was impressed by your further reference to Wiberg, I didn't notice that, at the same time as saying that the coinage metals are noble (unreactive) [their italics], Wiberg says at the foot of the page 1248, "The coinage metals... may also be extracted from their ores at relatively low temperatures. Of the 8 noble metals (6 platinum metals + Ag + Au), silver is the most abundant."

There are so many other sources referring to Cu as a noble metal that Zaki Ahmed is neither here nor there. A way to regard Cu is, I suggest, as the most reactive or humble of the noble metals per Makhlouf & Barhoum (1966) or Rohrig (2020).

More to follow. Sandbh (talk) 07:12, 31 March 2022 (UTC)
 * Okay, this is convincing. I guess some authors still do call Cu noble, even if it doesn't seem noble enough to my personal taste. :) Double sharp (talk) 08:15, 31 March 2022 (UTC)
 * First, let me convey my appreciation for the effort you've put into this. I certainly didn't intend for this to drag out this much.  Anyways, I ask that you look closely at the information you've just cited in light of my last comments.  I am not objecting to copper being called a noble metal.  *I* call it a noble metal.  I don't put it into this historically developed class of noble metals without qualification, however, and I don't think others do (which was my point with the Ahmed ref.) with one exception.  I think that your research here supports that view.  Looking at the 30 references you just cited, how many actually give a list of noble metals?  I mean an actual list.  There seems to be < 10 members of the group, so it should be possible to easily list them.  I count maybe 4 of them out of 30.  References #7 and #20 may be intended as a lists, with #7 excluding copper and #20 clearly discussing marine environments with Al and Ta included.  So, that leaves only #9 and #13 clearly named/intended as comprehensive lists of the noble metals.  Adding that to the 4 lists we already found, that gives a total of 6 lists.  None of these 6 list copper.
 * This is my point. If you find a list, again as in "The noble metals are...", I am now skeptical that any of them list copper.  If you think that, for instance, ref #2 fulfills that requirement and that it just doesn't consider Pt et al. as noble metals, I guess I wouldn't see the flaw in that reasoning, but I'd really doubt that that was what was intended.
 * The exception for which I think you have a number of strong support items for is that a significant group obviously considers the coinage metals (copper, silver, gold) as a sub-group of noble metals. I can certainly understand why that would be true.
 * What I think would both make sense and capture this information from an article perspective would be to list the noble metals in the opener per the 6 references which actually give lists stated as "The noble metals are usually listed as the 6 platinum metals plus Au with Ag, Re, and Hg also being in included on some lists." The history and meaning section could then explain (via the references) the fact that it is an ill-defined group and there is not a single criteria and that, for example, all the coinage metals are considered by some to be noble while others may specifically exclude copper (as at least 4 references explicitly do) or silver.  I would delete the "more inclusive lists" line currently present.  Then I would change the periodic table to highlight the inclusion of Cu and Ag with one of the authoritative coinage metal references.  Finally, in the table I would change the Brooks and Hamalainen references to be more authoritative books, which I think one of those above must cover.
 * These are just my suggestions. I think at this point that you must understand what I considered to be misleading and what I was trying to correct/clarify with my initial changes.  I accept that you are more experienced and probably a better judge of how to best go about this.  So, I will leave it to you at this point.  (If there are changes you want me to make changes, I can try.)  Again, I appreciate all the time and effort which I know you've put into this work.  Best Regards.     A15730 (talk) 15:54, 31 March 2022 (UTC)

, : We're close to what's going on, with the five "groups" of Huang 2018, including seminoble metals. Huang seems to have picked up from Tomashov & Matveeva 1968, and Tomashow et. al. 1966:


 * {| class="wikitable"

!"Group" !! E° !! Name || Examples
 * 1 || < –0.414 ||Active metal || Mg, Zn, Fe
 * 2 || –0.414 V < E° < 0 V || Second active || Cd, Ni, Pb
 * 3 || 0 V < E° < 0.815 V || Seminoble || Sn, Cu, Ag
 * 4 || 0.815 V < E° < 1.23 V|| Noble || Pd, Ir
 * 4 || E° > 1.23V || || Au
 * }
 * 4 || 0.815 V < E° < 1.23 V|| Noble || Pd, Ir
 * 4 || E° > 1.23V || || Au
 * }
 * 4 || E° > 1.23V || || Au
 * }

Alchemically, gold and silver were regarded as noble metals. The PGM were discovered later and seemed to have been added to the list of noble metals in light of their comparably inert nature. Tomashow et. al. 1966 imply that Ag is not really a noble metal but count it anyway on traditional grounds; then Tomashov & Matveeva 1968 refer to Ag as a seminoble metal; then Huang 2018 confirms this; and Rayner-Canham 2018 likewise picks up on Ag being too reactive.

Hg has its own problems as it wasn't admitted to the metal club until after, at the earliest, its solidification by cold was observed in 1759–60.

There seems then to have been eight traditional noble metals namely Au,Ag + the six PGM. And then there are the various "hangers on": Re, Cu, Hg and maybe Bi, all of which count as seminoble metals.

As noted, there seems to have been some conflation in the literature of coinage metals with noble metals hence the references to Cu. This has not been helped by the physics-based defintion of Cu-Ag-Au as noble metals cf the physic-based inclusion of As and Sb as metals.

Probably, the PT extract could show the big 7 + Cu, Ag, Re, Hg and Bi as the sometimes or somewhat noble metals. It's interesting that according to the table, only six metals count as noble metals (Pd, Os, Ir, Pt, Au and Hg) with another 6 (Cu, Ru, Rh, Ag, Re, Bi) as seminoble metals. Sandbh (talk) 02:30, 1 April 2022 (UTC)
 * By this definition, I guess Po is seminoble too. Also As, Sb, Te for those who would add some or any of them to metals. Double sharp (talk) 02:40, 1 April 2022 (UTC)

Po ought perhaps not be counted as a noble metal of any kind on account of its radioactivity. But perhaps it's worth a note. As, Sb perhaps in a cross-hatch; Te perhaps not unless we are going to admit semiconductors into the metal club. Sandbh (talk) 03:23, 1 April 2022 (UTC)


 * Looking through the 18th century literature, they had the equivalent notion of Hg as a seminoble metal. So whereas the perfect or noble metals Pt, Au, Ag were, according to them, not acted upon by air or water, at least Hg was acted upon by air. OTOH, Hg could be recovered from its oxide by heating. So Hg had a foot in both camps, being referred to sometimes as a noble metal and in other sources as a base metal. I guess this prevarication carried over into later sources, with Hg sometimes or sometimes not being counted as a noble metal. So HgO can be made by heating Hg in oxygen at roughly 350 °C. Conversely, in 1774, Priestley discovered that oxygen was released by heating mercuric oxide, although he did not identify the gas as oxygen (rather, Priestley called it "dephlogisticated air," as that was the paradigm he was working under at the time). Like silver, Hg too reacts with atmospheric hydrogen sulfide.


 * An odd situation. So I think still at least show the big 7 + Cu, Ag, Re, Hg and Bi as the sometimes or somewhat noble metals, depending on the criteria. So yes, Hg is a "group 4" (noble metal) but OTOH it doesn't cut the mustard in other respects. Sandbh (talk) 04:30, 1 April 2022 (UTC)

More to clean up
About the OP and the top periodic table illustration:
 * As presented, noble gases appear as "noble metals" too. This better be prevented (not by legend/text, but in graphics also).
 * The synthetic elements, or those with unknown relevant propertyies, better be marked as such. For example, so as not to imply a break in the groups but as unknown territiry. -DePiep (talk) 05:30, 1 April 2022 (UTC)
 * As noted, this is not the improvement proposed. The lede/top image only needs to convey: "What is ...". The side-information now crammed into it has its place in a section only. -DePiep (talk) 07:45, 1 April 2022 (UTC)

For now, I'm happy with what's there. Sandbh (talk) 10:16, 1 April 2022 (UTC)
 * For after now, we'll change it then. OK. -DePiep (talk) 18:08, 2 April 2022 (UTC)
 * I somewhat agree with DePiep on this one. It should be made more clear IMO that the noble gases and metalloids, while coloured in the table, are not "noble metals" according to anybody. With the exception of antimony, since one of Sandbh's sources (#11, Tomashov and Matveeva 1968) explicitly includes it. The noble gases make sense to talk about as a comparison, but since they are all in group 18 anyway, I'm not sure they need to be called out explicitly by colour. Metalloids don't really make sense here AFAICS. Then colour can be left to simply describe who calls what a noble metal, just as at Metals close to the border between metals and nonmetals.
 * As for radioactives, none of the sources provided above include them, even if they would satisfy the criteria. Polonium is a case in point: by its electrode potential, it ought to be a "semi-noble metal". But for most practical purposes when nobility is an important factor, radioactivity is a no-no. Superheavies have been referred to as "noble metals", but only as an expectation – nobody has been able to find out experimentally. They are also enough of a niche thing compared to the stable elements that I think it might be better to just chop off period 7 from the extract and leave the text to say something about their ambiguous status. Double sharp (talk) 04:16, 3 April 2022 (UTC)
 * Thanks for this expansion. Obviously, these details from the top image were not this clair at first (ten) sights.
 * So the article is to describe noble metals, and probably also also as opposed to: metalloids, noble gases, SHEs, radioactives.
 * (2) My point is: (1) the top image is to point out/illustrate/show the noble metals full stop. That also means: no distractions, no side details, and no owners hobbies.
 * The related subtopics, ie non metals vis-a-vis NGs etc, are to be treated separately, and so no be present in the top image. The top (lede) image is not to fold the whole article into. That is, assuming they are corrctly preset in the article. They could lead to some lines in the lede, but not more that 50% of that. All in all, it should serve our encyclopedic goal. -DePiep (talk) 07:15, 3 April 2022 (UTC)
 * For the lede image, I'd prefer to colour only the basic situation:
 * Ru, Rh, Pd, Os, Ir, Pt, Au: included by everyone
 * Cu, Ag, Sb, Re, Hg, Bi: included by some sources but not all.
 * That seems simple enough. Then the text can do the work explaining that some people have different criteria, some have other subclasses, historical evolution of the concept, etc. etc. etc. Double sharp (talk) 07:21, 3 April 2022 (UTC)
 * Yes, my thoughts too. Two gradient colors to illustrate like "sure" and "sometimes" &tc. Adding: not only history etc, but also the relationship with noble gases &tc &mdash;if viable for the article&mdash; to be moved into a (sub)section, not crammed in the lede/-image. -DePiep (talk) 12:53, 3 April 2022 (UTC)

I agree with two gradients. For the "sometimes" gradient only Cu, Ag, Re, Hg. I've not seen any source refer to Sb or Bi as actual noble metals, nor Po for that matter. However there are sources that note that at least Tc, As, Sb Bi, As and Po have some noble character. For Po, it would be counted as a genuine noble metal but for its radioactivity being self-defeating (Pourbaix 1974, p. 575):


 * "Thus, by converting the oxygen of the air into ozone, it causes the polonium to be oxidized in the presence of media which ought not to oxidize it, taking into consideration the noble character of the element; such media are air, acid solutions (HCl, HNO3, H2SO4, CH3CO2H, C2O4H2) and caustic alkali solutions (KOH, NaOH) [2]. It is a question, of course, of a secondary action of the α-radiation, but this does not make it any less fundamental in its results."

So perhaps three gradients: seven × sure (Ru, Rh, Pd, Os, Ir, Pt, Au); four × sometimes (Ag, Cu, Re, Hg); and five × seminoble (Tc, As, Sb, Bi, Po).

And yes, I'll remove the metalloid and NG gradients. Sandbh (talk) 07:10, 4 April 2022 (UTC)
 * Won't need three flavors: too much detail for a lede graph. Even today the colors are not nuanced (just a list of ~four: the "sometimes ..." are equal at this level). In the article, this can make more sense --though I could expect no grouping of these even there, just an author-link. IOW, in the article the authors can stay distinct. HTH. -DePiep (talk) 18:58, 4 April 2022 (UTC)
 * Showing the "sometimes" as being equal would not be representative of the literature. The lede should not dump accuracy in favour of simplicity. It happens that the literature on noble metals is messy, so the best that can be done is to at least distinguish between the metals effectively all authors agree are noble, and the sometimes noble metals. It does not help that the sources are contradictory e.g. some count eight noble metals including silver whereas some count only seven, excluding silver. Sandbh (talk) 02:05, 5 April 2022 (UTC)

Comments cont.
More on history.


 * Hopkins J 1918, "Earliest Alchemy", The Scientific Monthly, vol. 6, no. 6, pp. 530–537 (534):


 * In the elements of Empedocles, the sequence was from the lowest to the highest: earth, water, air, ﬁre. Following this order, the alchemists had the base metals, earthy; the fusible metals (like tin and mercury) having the property of liquidity; the bright or "noble" metals (gold and silver) remaining clear like air; and the bronzes of a higher spiritual nature, playing like ﬁre on the surfaces of the metals. Between the base metals, such as lead and copper, and the noble metals came tin, and later mercury, considered stages of transmutation.

So Cu was a base metal, and Hg was a fusible (not noble) metal.

While Pt wasn't discovered until 1735 it came to be recognised as a noble metal, alongside Ag and Au.

The rest of the PGM appeared much later: Pd 1802; Ir, Os 1803; Rh 1804; Ru 1844; Re 1928. I presume a textbook dated 1810–1850 or so would only recognise six noble metals. Three or four noble metals?


 * Cronstedt AF 1788, An Essay Towards a System of Mineralogy: In Two Volumes, vol. 2, p. 507:
 * …the noble metals, viz. platina, gold, and silver…Quicksilver holds a kind of middle place; for, like the base metals, it may be calcined, though not readily; and like the noble ones, it may be reduced by heat alone….we may therefore reckon four noble or perfect metals; viz gold, platina, silver, and mercury; because, when calcined, they recover their phlogiston, without the addition of any phlogistonic substance.

In the following extract from 1838, there are only seven noble metals including Ag, since Ru had not been discovered yet.


 * Griffin JJ 1838, Chemical Recreations: A Compendium of Experimental Chemistry, Part 1, pg. 143


 * Most of the metals fuse before the blowpipe, and, excepting the noble metals, become oxidised on exposure to the outer flame. Of the noble metals, Gold and Silver both melt, without suffering any further alteration. Platinum, iridium, palladium, rhodium, and osmium are all infusible; but the last by exposure to the outer flame, becomes oxidised, and volatises in the state of osmic acid.

We know that silver leaf was employed in illuminated manuscripts but was subject to corrosion.


 * Shaw H 1866, Handbook of the Art of Illumination, as Practised During the Middle Ages p. 59:


 * The metal next in importance to gold is silver, which was employed in illuminations of all periods, but more largely in drawings of an early date than in those of a later time…The original beauty and brilliancy of these…have been sadly marred by the blackened state of the silver from oxidation.
 * In more recent examples we have met with many instances in which this metal has retained in a remarkable manner its original freshness. We would particularly allude to the prayer-book of Henry VI…The almost unchanged appearance of he drawings in these books could only arise from their being rarely exposed to the action of light and atmospheric influences, or to the silver having being fixed to the vellum in leaves on a preparation of size, and secured from all sinister action on its surface by the protection of a varnish.

More on copper as a seminoble metal.


 * Ostwald W 1906, Conversations on chemistry, vol. 2, p. 315, 337:


 * Copper…may be looked upon as representing the transition stage between the base and noble metals.


 * You already know mercury so well that all I have to do to complete the description of its properties...is only to give you a few ﬁgures…At the ordinary temperature neither damp nor dry have any effect on it, but it oxidizes at or about 300°. However, the mercuric oxide, when subjected to a greater heat, decomposes, as you know, into the metal and oxygen. Therefore, the adjective noble may be applied to mercury for all practical purposes."

Perhaps sometime in the 1930s, the physics-based definition of a noble metal as being Cu, Ag, Au arises. Here's a sample extract:


 * Seitz F & Johnson RP 1937, Modern theory of solids. II,. Journal of Applied Physics, vol. 8, no. 3, 186–199 (194)


 * …using the zone theory, that in the alkali metals and the noble metals (Cu, Au and Ag)…

And then there is the confusion with precious metals.


 * Anusavice DMD, ‎Chiayi Shen ‎H & Dawls R 2012, Phillips' Science of Dental Materials, p. 369:
 * These [seven] noble metals and silver are sometimes called precious metals, referring to their high economic value, but the term precious is not synonymous with noble. Silver is reactive in the oral cavity and is not considered a noble metal.

Here's a good defintion of the term.


 * Louis C & Pluchery O 2017, Gold Nanoparticles For Physics, Chemistry And Biology, p. 393:
 * …gold has long been considered as an inert material since bulk gold does not react with many molecules typically present in the ambient atmosphere, the property that renders gold the most noble metal.

Sandbh (talk) 07:26, 3 April 2022 (UTC)

The picture becomes clearer
,, I'd wondered why Ag was ever regarded as a noble metal given that when sulfur is present, usually as hydrogen sulfide, it reacts with silver to form the well-known tarnish of Ag2S. It transpires that from about the middle of the 19th century onwards (at least in the US) sulfur levels increased by up to 25 times, due to the industrial revolution/s, peaking in about 1920, and staying at that level until falling away after about 1980, when stricter sulfur emission standards were adopted in parts of the world. That's why it came to be that silver plate or silver wasn't used as extensively as it had been in the past. The rest of the noble metals i.e. the PGM + Au are not so affected at room temperature. That's why, I guess, while Ag was traditionally regarded as a noble metal back in alchemical times, it later came be dropped off of some lists of noble metals.

I've also found a source (Russell & Lee 2005, Structure-property relations in non-ferrous metals, p. 293) saying that the PGM, and their "exceptional resistance to oxidation and chemical attack in corrosive aqueous solutions", originates in their high EN, and does not rely on a protective oxide layer. The lack of an oxide film is also the case for Ag and Au neither of which react with O; Ag only reacts at a pressure of 1.5 MPa and 300 °C, caveating that Ag does not have an exceptional resistance to being oxidised by sulfides. The EN values are interesting: 1.9 Re; 1.93 Ag; Hg. 2.0; 2.2 Ir, Os, Pd; 2.28 Pt, Rh; 2.54 Au. One needs an EN of 2.2 or more, to be on the starting blocks. Unanswered question: why is W at 2.36 not a noble metal? Pourbaix says it is a base metal.

It seems that nearly all the other metals and metalloids form an oxide film on their surfaces when exposed to oxygen at RT. The only exception appears to be Ge which, in any event, is not noble in the electrochemical sense (GeO2 + 4e– → Ge = –0.25), and its EN at 2.01 falls short. Sandbh (talk) 08:05, 5 April 2022 (UTC)
 * I'm not convinced that the Pauling electronegativity for W is really correct. On the Allen scale it is much lower, in keeping with its neighbours (Ta 1.34, W 1.47, Re 1.60). If the Allen scale has a better handle on the real situation for Mo and W, then it would pretty neatly explain why tungsten is left off. Double sharp (talk) 08:13, 5 April 2022 (UTC)
 * Regarding why W is not a noble metal. I'm going to posit that there are four traditional tests which might make one think an element is a noble metal.  1.  I find it as a pure metal--  W is not found in pure form.  2.  I can purify the metal/reduce its oxide by heating it in air-- cannot be done with W.  3.  I have some aqueous reactivity criteria such as I put it into sulfuric and see if it bubbles, dissolves in nitric, etc.-- W resists being dissolved in acids very well, but can be dissolved in bases.  4.  I can put it into an aqueous solution and reduce it electrochemically to bulk, pure metal-- cannot be done with W.  Ag, on the other hand, definitely passes criteria #1 and #4.  A15730 (talk) 14:04, 5 April 2022 (UTC)

Full electrochemical series
For fun I decided to compile such a thing based on the NIST tables at Reactivity series. To be somewhat "fair", I picked only aqua cations (charge up to +4, to take into account things like thorium that don't form anything lower). The most stable was picked when there was a choice. The rows are greyed out when they are the result of a calculation or if the species itself are somewhat doubtful.

Not included are "I+" and "Rn2+" as just too unbelievable.

That said, for "safety" I would rather remove: 7th period (CRC and NIST give slightly different orders e.g. Pu vs Be); At (radioactivity problem again and not even sure to be a real aqua complex); Ge (not even physically a metal); Zr–Tc and Hf–Os (cation is either too highly charged or too doubtful).

And yes, I did notice that it matches reactivity better if you use Eu2+ rather than Eu3+, but the latter is more stable. Double sharp (talk) 08:44, 5 April 2022 (UTC)
 * Okay, I cut most of those out. Though I left germanium, since it might form an aqua cation in very acidic conditions anyway. You can see the "completionist's version" here.
 * The noble and semi-noble metals can be found on the bottom. If we included "dubious" cations, then Os appears with the noble metals as expected; Tc, W, Re are added to semi-noble metals. (And Ge I suppose, but it's not a metal.) At probably appears as a true noble metal, but clearly its radioactivity would spoil that in dramatic fashion.
 * Of course this order is not everything: Ru and Rh appear below Ag, but Ag is more reactive. Double sharp (talk) 08:56, 5 April 2022 (UTC)

Noble metals in physics
and, thanks for your further thoughts.

I've been puzzling out why the physicists refer to noble metals as Cu-Ag-Au. It looks like they do this because they're actually referring to the monovalent noble metals, +1 being a state Cu-Ag-Au are all known in.

In the chemistry literature there are references to Cu being counted as a noble metal pre-dating the physics-based mention of the noble metals as Cu-Ag-Au. And Cu for sure has a positive standard electrode potential and counts as being noble in this sense.

As far as I've been able to ascertain, it remains the case that the noble metals are, in the modern sense, most popularly thought of as Au and the PGM since they're the only metals that don't tarnish in dry or most air at room temperature.

Tomorrow I intend to compile an informal list of noble metal lists. Sandbh (talk) 08:24, 10 April 2022 (UTC)
 * Does Ag tarnish in the absence of sulfur? Double sharp (talk) 08:27, 10 April 2022 (UTC)


 * , no, it doesn't.


 * That said, Ag (and Hg) are usually found in nature as sulfides. Whereas Au and the PGMs, AFAIK, are usually found native and often associated with one another. Perhaps then there are four tiers of noble metals, with the higher three providing informal criteria for noble metal status:


 * {| class="wikitable"

! Tier !! Criterion !! # !! Metals
 * + "Noble metals"
 * 0 || Base metals that behave like noble metals due to surface passivation || ? || e.g. Al, Cr, Ta
 * 1 || Positive redox potential || 16 || Sb,* As,* Re, Tc, Bi, Cu, Po, Ag, Hg, PGM and Au
 * 2 || Don't react with O in ordinary conditions || 9 || Ag, Hg, PGM, Au
 * 3 || Usually found in native form || 7 || PGM + Au
 * }
 * &ast; if classed as a metal
 * 3 || Usually found in native form || 7 || PGM + Au
 * }
 * &ast; if classed as a metal
 * &ast; if classed as a metal


 * Tier 1 is good since that is one (the rudimentary) way noble metals are thought of.
 * Tier 3 seems to be the one that sorts the gloss from the dross.


 * I see that Sb, As, Bi, Cu, Ag and Hg are chalcophiles whereas PGM + Au = siderophiles. Now that I think about it, that shouldn't surprise me given the susceptibility of Ag to attack by S.


 * The variability in the literature arises from the usual habit of relying on a single criterion. I was reminded of this by the following passage:
 * "As the [periodic table] arrangement groups together elements of similar properties, we should naturally expect that the property of valency would find some expression therein; since, however, this property is so complex we should hardly look for a perfect illustration of it in a table based, in the first instance, upon a single property of the elements. But we may say that the elements of any one group exhibit the same valency, whilst in any one [horizontal] series a regular increase in the valency of the elements accompanies the increase of atomic weight; and it will further be seen that the valency, as shown by the oxides, increases from one to eight as we pass from Group I to VIII but, as shown by the hydrides (or halides), it rises to a maximum of five and then falls to one; both rise and fall are regular."


 * Lewis EI 1914, Inorganic Chemistry, Part 1, 2nd ed., Cambridge University Press, pp. 386–387
 * --- Sandbh (talk) 02:16, 11 April 2022 (UTC)
 * Re is a siderophile too, and enough of one to be very rare in the crust. Os certainly reacts with oxygen when finely divided. And don't Cu and Ag also have significant native occurrence?
 * I kind of think now that notions like 'metal', 'noble metal', etc. are inherently fuzzy, having circles of better and worse examples. So Au is a canonical example of most ideas of "nobility", and as you descend from that, you get some better and some worse examples, which somewhat depend on criteria (e.g. electrochemically Ag is more noble than Rh, but in terms of inertness to a variety of attacking gases, it's rather the other way round). So it's not a bad thing that they vary by author and don't quite have a canonical all-seasons definition. But YMMV. Double sharp (talk) 03:00, 11 April 2022 (UTC)

Re tarnishes slightly at room temperature in moist air. Os is stable, unless heated or finely divided. I suspect Cu and Ag usually occur as sulfides and less so natively, but I haven't researched this point yet. Your idea of circles of better and worse examples has merit. Sandbh (talk) 01:27, 12 April 2022 (UTC)


 * Weaver & Foster (1960) in Chemistry for our times, pp. 610–611 write, "Silver occurs free, but the sulfide ore, argentite (Ag2S), found with copper and lead sulfides, is the most important source" and that, "Silver does not combine directly with oxygen but does form an oxide (Ag2O) with ozone, at room temperature. The oxide decomposes on gentle heating (260°C)." Sandbh (talk) 07:15, 13 April 2022 (UTC)

NB: The question of why physics confines the noble metals to Cu-Ag-Au is continued at WP:PHYSICS talk. Sandbh (talk) 06:49, 16 April 2022 (UTC)

Zumdahl (1993)
, I’ve checked 201 books so far (1925 to 1993) and found 45 hits for noble metals = 22.4%.

Zumdahl, in Chemistry, (1993, 3rd, ed., p. 834) had something interesting to say about the topic:


 * "Some metals, such as copper, gold, silver, and platinum, are relatively difficult to oxidise. These are often called noble metals.
 * Corrosion can be viewed as the process of returning metals to their natural state—the ores from which they were originally obtained. Corrosion involves oxidation of the metal. Since corroded metal often loses its structural integrity and attractiveness, this spontaneous process has great economic impact. Approximately one-ﬁfth of the iron and steel produced annually is used to replace rusted metal.
 * Metals corrode because they oxidize easily. Table 17.1 shows that, with the exception of gold, those metals commonly used for structural and decorative purposes all have standard reduction potentials less positive than that of oxygen gas. When any of these half-reactions is reversed (to show oxidation of the metal) and combined with the reduction half-reaction for oxygen, the result is a positive E° value. Thus the oxidation of most metals by oxygen is spontaneous (although we cannot tell from the potential how fast it will occur).
 * In view of the large difference in reduction potentials between oxygen and most metals, it is surprising that the problem of corrosion does not completely prevent the use of metals in air. However, most metals develop a thin oxide coating, which tends to protect their internal atoms against further oxidation. The metal that best demonstrates this phenomenon is aluminium. With a reduction potential of –1.7 V, aluminium should be easily oxidized by O2. According to the apparent thermodynamics of the reaction, an aluminium airplane could dissolve in a rainstorm. The fact that this very active metal can be used as a structural material is due to the formation of a thin, adherent layer of aluminium oxide (Al2O3), more properly represented as Al2(OH)6, which greatly inhibits further corrosion. The potential of the “passive,” oxide-coated aluminium is –0.6 V, a value that causes it to behave much like a noble metal.
 * Iron also can form a protective oxide coating. This is not an infallible shield against corrosion, however; when steel is exposed to oxygen in moist air, the oxide that forms tends to scale off and expose new metal surfaces to corrosion.
 * The corrosion products of noble metals such as copper and silver are complex and affect the use of these metals as decorative materials. Under normal atmospheric conditions, copper forms an external layer of greenish copper carbonate called patina. Silver tarnish is silver sulfide (Ag2S), which in thin layers gives the silver surface a richer appearance. Gold, with a positive standard reduction potential of 1.50 V, significantly larger than that for oxygen (1.23 V), shows no appreciable corrosion in air."

The following caught my eye:
 * 1) Thinking of corrosion as returning the elements involved to their natural state.
 * 2) The table of SRP values includes Hg (0.80) but not As, Sb, or Bi.
 * 3) Mention of a passivated Al potential, although it's not clear why a potential which is still negative would cause it to behave much like a noble metal.
 * 4) Saying noble metals are "relatively" difficult to corrode and OTOH saying the corrosion products of Cu and Ag affect their use as decorative materials.
 * 5) The reference to the SRP of oxygen makes Huang (extract #31) clearer for me. Sandbh (talk) 02:02, 12 April 2022 (UTC)
 * Number 1 amusingly makes me wonder what hypothetical Mercurians would consider "noble", considering that that planet seems to have formed in a very reducing environment and it shows in the minerals there (sulfides rather than sulfates). I wonder if there are any base metals that react strongly with oxygen but not with sulfur... Double sharp (talk) 03:45, 12 April 2022 (UTC)
 * Hmmm, Mercury has almost no atmosphere, and a crust largely made up of Mg–Fe–Ca-rich sulfides. If it did have an atmosphere it'd contain practically no oxygen. If there was some H2S in the atmosphere I don't know that this would matter since the reaction of silver with H2S requires the presence of oxygen. I see the average temperature on Mercury is 452 K, and that sulfur melts at 318 K, which may suggest there's no free sulfur on Mercury. I just don't know how e.g. silver would behave in the presence of H2S at 452 K, and in the absence of oxygen. Sandbh (talk) 06:48, 14 April 2022 (UTC)
 * For base metals that react strongly with O but not (so much) with S, Ac has super-high oxophilicity but below the bottom of the scale thiophilicity, see Kepp, K. P. (2016). A quantitative scale of oxophilicity and thiophilicity. Inorganic Chemistry, 55(18), 9461–9470, table 1, p. 9643, Sandbh (talk) 04:29, 19 April 2022 (UTC)

Proposed cleaned-up illustration
[[File:PT extract noble metalsN.png|thumb|upright=2.1|

 Periodic table extract showing approximately how often each element tends to recognized as a noble metal: 

 The thick black line encloses the seven to eight metals most often to often so recognized.  † attacked by sulfur or hydrogen sulfide § self-attacked by radiation-generated ozone ]], : Based on an informal audit of 267 chemistry books (1925–2018), in 57 of which (21.3%) I was able to find mention of noble metals.
 * may be tarnished in moist air or corrode in an acidic solution containing oxygen and an oxidant

The thick black border:
 * encompasses all the metals with a SRP > 0.4 V, except for Hg and Po; all other shaded elements have positive potentials (but < 0.4) and are noble in that sense.
 * encloses "the" noble metals, with the partly dashed lines around Ag trying to accommodate differing views on whether Ag is or is not a noble metal; I'll need to elaborate this in the caption to the image.

I'll leave in the super-heavies for completeness, and say something about their status in the article.

The legend will go into the caption, once I figure out the best way to add supporting sources. Sandbh (talk) 08:22, 12 April 2022 (UTC)


 * An impressive amount of work there. I'm not sure about this change though.  As you know, what I didn't like about the article originally was that, in my mind, it read as putting Cu too close to Au.  This calls Au a "nearly always" while Cu is a "sometimes" whereas I think Au is an "always" while Cu is an "it depends on your definition".  That said, I don't have a better suggestion, and I think this is obviously a tremendous improvement over what was there before.  If it's clear to you and Double sharp, go with it.
 * With regards to the standard reduction potentials, those would be of relevance when seeing if the metal is attacked by weak acids or the like and are critical in the corrosion sciences where the reactions of greatest importance are those occuring in natural waters. In the classical chemistry field, however, I suspect that oxidation in nitric acid would have carried weight because it is more readily observable in a short time period.  e.g.  A still used test to determine unknown metal coatings in the surface finishing industry is to first try to dissolve in 50% nitric.  If yes, blue is copper or alloy, green is nickel, etc.  If it doesn't dissolve, then try hydrochloric acid which will sort out some of the base metals that passed step one due to passive oxides.  Then try a nitric/hydrochloric mix.  (Silver doesn't pass step one, while the "less noble" Pt group metals do.)
 * My point with this is merely to highlight that a knowledge of the background of the person and where they are at in history is useful in understanding/knowing what they think is a noble metal and why. To that end, I think it would be fantastic if you could synthesize some of your findings with the meaning and history section as well.  Best Regards. A15730 (talk) 02:08, 13 April 2022 (UTC)
 * The two rectangle types are not explained. Also, they complicate (or even contradict, see also previous image). -DePiep (talk) 06:58, 13 April 2022 (UTC)
 * I like this and think it's a significant improvement. Perhaps something in the caption should explain the thick lines for the main cluster? Also, oganesson (118) is misspelled. :) Double sharp (talk) 04:21, 14 April 2022 (UTC)
 * There are two lines yet to be clarified. Still, that is a complication (2-dimensional meaning set), which is not warranted in this place. Also: since it is an extract from the periodic table, so the PT is context, one more group to the ;left should be included (there too illustrating which PT area is not included).
 * Questions raised by A15730 are still to be taken care of. -DePiep (talk) 05:49, 14 April 2022 (UTC)
 * Yes, I agree that there should be another group to the left to show where the noble-metals range stops. But while I don't think this is perfect, I still think it's better than what we had before. :) Double sharp (talk) 07:11, 14 April 2022 (UTC)
 * Thanks A15730, DePiep, Double sharp, I've fixed the image and moved the legend into a caption. I was at a library today (that I hadn't been able to visit for quite some time) and have a few more thoughts to follow, including about nitric acid. Sandbh (talk) 08:14, 14 April 2022 (UTC)
 * A15730, Acting on your concern about Au, the image now shows that Pt and Au are always regarded as noble. On standard reduction potentials I hadn't intended to attach too much importance to this. I mentioned it as more of a passing comment i.e. that it was a happy outcome that the 7 to 8 metals commonly recognised as noble all had values > 0.4 V. I'll have to wait and see how much importance is attached to SRP once I start on polishing the text of the article. The nitric acid angle is interesting; is a 50% concentration counted as weak nitric acid? FYI: Double sharp.
 * --- Sandbh (talk) 04:12, 16 April 2022 (UTC)
 * There are still three graphical indicator sets. One is not explained at all (dashed line), one has shifting criteria ('limited sense' is changed scale range), * † § introduce unrelated criteria. As an introductionary image it fails primary encyclopedic requirements. Looks like the whoile article is crammed into this one? -DePiep (talk) 04:53, 26 April 2022 (UTC)
 * , thanks for looking. The image now has one solid line. The first sentence in the article has been updated so that * † § now make sense. The frequency of recognition adjectives have been adjusted so there's no more shifting criteria. Sandbh (talk) 00:04, 28 April 2022 (UTC)
 * I wasn't quite right. There is still a "limited sense" category. I'll look at that again. Sandbh (talk) 00:06, 28 April 2022 (UTC)

Updated lede and image
, : As a culmination of this thread I've updated the article lede and image, temporarily trimmed the EN v MP image which was taking too much room, and trimmed rhenium from the image gallery. I hope you'll be OK with this. The rest of the article will need more work, including as outlined by A15730, which I expect'll occur slowly. I temporarily trimmed mention of semi-noble metals at least until the basics of the article get better. Sandbh (talk) 07:30, 24 April 2022 (UTC)

"Sulfur" used in article instead of "sulphur"
I am not sure why, but presently the article uses "sulfur" despite the article being tagged "use British English". Collins and Oxford both cite "sulphur" as correct in BrE and "sulfur" as being US English. 81.96.145.214 (talk) 10:16, 25 August 2023 (UTC)


 * This is the standard international spelling used worldwide in chemistry and in Wikipedia chemistry articles, regardless of the variety of English in the article. See WP:SULF. --Ben (talk) 15:37, 25 August 2023 (UTC)
 * Apologies, I did not know about that policy. 81.96.145.214 (talk) 21:30, 25 August 2023 (UTC)