Editing Group 9 element (section)

{{Short description|Group of chemical elements}}
{{Infobox periodic table group
| title       = Group&nbsp;9 {{nowrap|in the periodic table}}
| group number= 9
| trivial name= 
| by element  = cobalt group
| CAS         = part of VIIIB
| old IUPAC   = part of VIII
| mark        = Co,Rh,Ir,Mt
| left        = [[Group 8 element|group 8]]
| right       = [[Group 10 element|group 10]]
}}
{| class="floatright"
! colspan=2 style="text-align:left;" | ↓&nbsp;<small>[[Period (periodic table)|Period]]</small>
|-
! [[Period 4 element|4]]
| {{element cell image|27|Cobalt|Co| |Solid|Transition metal|Primordial|image=Kobalt electrolytic and 1cm3 cube.jpg|image caption=Cobalt, electrolytic made, 99,9%}}
|-
! [[Period 5 element|5]]
| {{element cell image|45|Rhodium|Rh| |Solid|Transition metal|Primordial|image=Rhodium powder pressed melted.jpg|image caption=Rhodium, powder, pressed, remelted 99,99%}}
|-
! [[Period 6 element|6]]
| {{element cell image|77|Iridium|Ir| |Solid|Transition metal|Primordial|image=Iridium-2.jpg|image caption=Pieces of pure iridium}}
|-
! [[Period 7 element|7]]
| {{element cell image|109|Meitnerium|Mt| |Unknown phase|Unknown chemical properties|Synthetic|legend=unknown chemical properties}}
|-
| colspan="2"|
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''Legend''
{| style="margin-left: auto; margin-right: auto; text-align:center; border:0;"
|-
| style="border:{{element color|Primordial}}; background:{{Element color|table mark}}; padding:0 2px;" | [[primordial element]]
|-
| style="border:{{element color|Synthetic}}; background:{{Element color|table mark}}; padding:0 2px;" | [[synthetic element]]
|}
|}

'''Group 9''', by modern [[Group (periodic table)#CAS and old IUPAC numbering (A/B)|IUPAC]] numbering,<ref>{{cite journal |last1=Fluck |first1=E. |year=1988 |title=New Notations in the Periodic Table |url=http://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] |volume=60 |issue=3 |pages=431–436 |doi=10.1351/pac198860030431 |access-date=24 March 2012 |s2cid=96704008}}</ref> is a group (column) of [[chemical element]]s in the [[d-block]] of the [[periodic table]]. Members of Group 9 include [[cobalt]] (Co), [[rhodium]] (Rh), [[iridium]] (Ir) and [[meitnerium]] (Mt).<ref name=leigh>Leigh, G. J. ''Nomenclature of Inorganic Chemistry: Recommendations 1990''. Blackwell Science, '''1990'''. p. 283. {{ISBN|0-632-02494-1}}.</ref> These elements are among the rarest of the [[transition metal]]s,<ref>{{Cite web |date=2020-08-15 |title=Group 9: Transition Metals |url=https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Supplemental_Modules_and_Websites_(Inorganic_Chemistry)/Descriptive_Chemistry/Elements_Organized_by_Block/3_d-Block_Elements/Group_09%3A_Transition_Metals |access-date=2022-03-24 |website=Chemistry LibreTexts |language=en}}</ref> and as of 2025 rhodium and iridium are the only non-radioactive metals with higher prices per weight than gold.<ref>{{Cite web |date=2025-03-20 |title=Spot metal prices in USD |url=https://www.dailymetalprice.com/metalpricescurr.php?x=USD |access-date=2025-03-20 |website=Daily Metal Prices |language=en}}</ref>

Like other groups, the members of this family show patterns in [[electron configuration]], especially in the outermost shells, resulting in trends in chemical behavior; however, rhodium deviates from the pattern.