Editing Noble metal (section)

=== Electrochemical ===
[[Standard reduction potential]]s in aqueous solution are also a useful way of predicting the non-aqueous chemistry of the metals involved. Thus, metals with high negative potentials, such as sodium, or potassium, will ignite in air, forming the respective oxides. These fires cannot be extinguished with water, which also react with the metals involved to give hydrogen, which is itself explosive. Noble metals, in contrast, are disinclined to react with oxygen and, for that reason (as well as their scarcity) have been valued for millennia, and used in jewellery and coins.<ref>G. Wulfsberg 2000, "Inorganic Chemistry", University Science Books, Sausalito, CA, pp. 270, 937.</ref>
{| class="wikitable sortable" style="font-size:90%; float:right; margin-left:20px"
|+ Electrochemical properties of some metals and metalloids
|-
!Element !! Z !! G !! P !! Reaction !! SRP(V) || EN||EA
|-
|| [[Gold]] ✣ || 79 || 11 || 6 || {{chem|Au|3+}} + 3&nbsp;e<sup>−</sup> → Au || 1.5 ||2.54|| 223
|-
|| [[Platinum]] ✣ || 78 || 10 || 6 || {{chem|Pt|2+}} + 2&nbsp;e<sup>−</sup> → Pt || 1.2 ||2.28|| 205
|-
|| [[Iridium]] ✣ || 77 || 9 || 6 || {{chem|Ir|3+}} +  3&nbsp;e<sup>−</sup> → Ir || 1.16 ||2.2|| 151
|-
|| [[Palladium]] ✣ || 46 || 10 || 5 || {{chem|Pd|2+}} + 2&nbsp;e<sup>−</sup> → Pd || 0.915 ||2.2|| 54
|-
|| [[Osmium]] ✣ || 76 || 8 || 6 || {{chem|OsO|2}} +  4&nbsp;{{chem|H|+}} + 4&nbsp;e<sup>−</sup> → Os + 2&nbsp;{{chem|H|2|O}} || 0.85 ||2.2|| 104
|-
|| [[Mercury (element)|Mercury]] || 80 || 12 || 6 || {{chem|Hg|2+}} + 2&nbsp;e<sup>−</sup> → Hg || 0.85 ||2.0|| −50
|-
|| [[Rhodium]] ✣ || 45 || 9 || 5 || {{chem|Rh|3+}} + 3&nbsp;e<sup>−</sup> → Rh || 0.8 ||2.28|| 110
|-
|| [[Silver]] ✣ || 47 || 11 || 5 ||  {{chem|Ag|+}} + e<sup>−</sup> → Ag || 0.7993 ||1.93|| 126
|-
|| [[Ruthenium]] ✣ || 44 || 8 || 5 || {{chem|Ru|3+}} + 3&nbsp;e<sup>−</sup> → Ru || 0.6 ||2.2|| 101
|-
|| [[Polonium]] ☢ || 84 || 16 || 6 || {{chem|Po|2+}} + 2&nbsp;e<sup>−</sup> → Po || 0.6 || 2.0 || 136 
|- style="background:orange"
|| Water || || || || 2&nbsp;{{chem|H|2|O}} + 4&nbsp;e<sup>−</sup> +{{chem|O|2}} → 4 OH<sup>−</sup> || 0.4 || || 
|-
|| [[Copper]] || 29 || 11 || 4 || {{chem|Cu|2+}} + 2&nbsp;e<sup>−</sup> → Cu || 0.339 ||2.0 || 119 
|-
|| [[Bismuth]] || 83 || 15 || 6 || {{chem|Bi|3+}} + 3&nbsp;e<sup>−</sup> → Bi || 0.308 ||2.02 || 91 
|-
|| [[Technetium]] ☢ || 43 || 7 || 6 || {{chem|Tc|O|2}} + 4&nbsp;{{chem|H|+}} + 4&nbsp;e<sup>−</sup> → Tc + 2&nbsp;{{chem|H|2|O}} || 0.28 ||1.9 || 53 
|-
|| [[Rhenium]] || 75 || 7 || 6 || {{chem|Re|O|2}} + 4&nbsp;{{chem|H|+}} + 4&nbsp;e<sup>−</sup> → Re + 2&nbsp;{{chem|H|2|O}} || 0.251 ||1.9 || 6 
|-
|| [[Arsenic]]<sup>MD</sup> || 33 || 15 || 4 || {{chem|As|4|O|6}} + 12&nbsp;{{chem|H|+}} + 12&nbsp;e<sup>−</sup> → 4 As + 6&nbsp;{{chem|H|2|O}} || 0.24 ||2.18 || 78 
|-
|| [[Antimony]]<sup>MD</sup> || 51 || 15 || 5 || {{chem|Sb|2|O|3}} + 6&nbsp;{{chem|H|+}} + 6&nbsp;e<sup>−</sup> → 2 Sb + 3&nbsp;{{chem|H|2|O}} || 0.147 ||2.05 || 101 
|-
|colspan=8|<small>'''Z''' atomic number; '''G''' group; '''P''' period; '''SRP''' standard reduction potential; '''EN''' electronegativity; '''EA''' electron affinity</small>
|-
|colspan=8|<small>✣ traditionally recognized as a noble metal; <sup>MD</sup> metalloid; ☢ radioactive</small>
|}
The adjacent table lists [[standard reduction potential]] in volts;<ref>G. Wulfsberg, "Inorganic Chemistry", University Science Books, 2000, pp. 247–249 ✦ Bratsch S. G., "Standard Electrode Potentials and Temperature Coefficients in Water at 298.15 K", ''Journal of Physical Chemical Reference Data,'' vol. 18, no. 1, 1989, pp. 1–21 ✦ B. Douglas, D. McDaniel, J. Alexander, "Concepts and Models of Inorganic Chemistry", John Wiley & Sons, 1994, p. E-3</ref> electronegativity (revised Pauling); and electron affinity values (kJ/mol), for some metals and metalloids.

The simplified entries in the reaction column can be read in detail from the [[Pourbaix diagram]]s of the considered element in water. Noble metals have large positive potentials;<ref name="Ahmad 2006 40">{{cite book |last=Ahmad |first= Z|date=2006 |title= Principles of corrosion engineering and corrosion control|location= Amsterdam|publisher= Elsevier|page=40 |isbn= 9780080480336}}</ref> elements not in this table have a negative standard potential or are not metals.

Electronegativity is included since it is reckoned to be, "a major driver of metal nobleness and reactivity".<ref name="Kepp"/>

The black tarnish commonly seen on silver arises from its sensitivity to sulphur containing gases such as [[hydrogen sulfide]]:

:2 Ag + H<sub>2</sub>S + {{sfrac|1|2}}O<sub>2</sub> → Ag<sub>2</sub>S + H<sub>2</sub>O.

Rayner-Canham<ref name="RC">{{cite book |last=Rayner-Canham|first=G|editor-last1=Scerri |editor-first1=E |editor-last2=Restrepo |editor-first2=G |title=Mendeleev to Oganesson: A multidisciplinary perspective on the periodic table |publisher=Oxford University |date=2018 |pages=195–205 |chapter=Organizing the transition metals|isbn=978-0-190-668532}}</ref> contends that, "silver is so much more chemically-reactive and has such a different chemistry, that it should not be considered as a 'noble metal'." In [[dentistry]], silver is not regarded as a noble metal due to its tendency to corrode in the oral environment.<ref>
{{cite book |last1=Powers |first1= JM|last2=Wataha|first2=JE|date= 2013|title= Dental materials: Properties and manipulation|location=St Louis |publisher= Elsevier Health Sciences|page= 134|isbn= 9780323291507 |edition=10th}}</ref>

The relevance of the entry for water is addressed by Li et al.<ref>{{cite book |last1=Li |first1=Y |last2=Lu|first2=D|last3=Wong|first3=CP|date=2010 |title=Electrical conductive adhesives with nanotechnologies |location=New York |publisher=Springer |page=179 |isbn=978-0-387-88782-1}}</ref> in the context of galvanic corrosion. Such a process will only occur when:
:"(1) two metals which have different electrochemical potentials are...connected, (2) an aqueous phase with electrolyte exists, and (3) one of the two metals has...potential lower than the potential of the reaction ({{chem|H|2|O}} + 4e + {{chem|O|2}} = 4 OH<sup><big>•</big></sup>) which is 0.4 V...The...metal with...a potential less than 0.4 V acts as an anode...loses electrons...and dissolves in the aqueous medium. The noble metal (with higher electrochemical potential) acts as a cathode and, under many conditions, the reaction on this electrode is generally {{chem|H|2|O}} − 4&nbsp;e<sup><big>•</big></sup> − {{chem|O|2}} = 4 OH<sup><big>•</big></sup>)."

The [[superheavy element]]s from [[hassium]] (element 108) to [[livermorium]] (116) inclusive are expected to be "partially very noble metals"; chemical investigations of hassium has established that it behaves like its lighter congener osmium, and preliminary investigations of [[nihonium]] and [[flerovium]] have suggested but not definitively established noble behavior.<ref>{{cite journal |last1=Nagame |first1=Yuichiro |last2=Kratz |first2=Jens Volker |last3=Matthias |first3=Schädel |date=December 2015 |title=Chemical studies of elements with Z ≥ 104 in liquid phase |journal=Nuclear Physics A |volume=944 |pages=614–639 |doi=10.1016/j.nuclphysa.2015.07.013|bibcode=2015NuPhA.944..614N |url=https://jopss.jaea.go.jp/search/servlet/search?5050598 }}</ref> [[Copernicium]]'s behaviour seems to partly resemble both its lighter congener mercury and the noble gas [[radon]].<ref name=CRNL>{{cite journal |last1=Mewes |first1=J.-M. |last2=Smits |first2=O. R. |last3=Kresse |first3=G. |last4=Schwerdtfeger |first4=P. |title=Copernicium is a Relativistic Noble Liquid |journal=Angewandte Chemie International Edition  |date=2019 |volume=58 |issue=50 |pages=17964–17968 |doi=10.1002/anie.201906966 |pmid=31596013 |pmc=6916354 |url=https://www.researchgate.net/publication/336389017|doi-access=free }}</ref>