Seeing Copper has an exceptional electron filling in its valence shell(4s1 3d10), the way I see it is that on +1, a d10 configuration should be more stable and hence easier to attain than a d9 which would come on +2. Or is there some reorganisation of electrons? Either way, please help explain. Thank you.

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    $\begingroup$ Also, I suppose your question refers to the scenario in an aqueous medium? $\endgroup$
    – PV.
    Commented Feb 26, 2021 at 5:41
  • $\begingroup$ I suppose so. I meant to ask why the +2 oxidation state for Copper is more common than its +1. I realise there is another question on the same topic, but i didn't understand their answer. Yours, I do. Is the greater tendency of hydration the only reason for greater stability of Cu+2 compounds? Or is there some rearrangement of energy at the electronic level? $\endgroup$ Commented Feb 26, 2021 at 8:37
  • $\begingroup$ Cu2+-2Z having higher hydrothermal stability than [Cu(OH)]+ is said to be the most contributing factor in attributing to its overall stability. This is found at : Related: osti.gov/pages/servlets/purl/1437018 $\endgroup$
    – PV.
    Commented Feb 26, 2021 at 11:37
  • $\begingroup$ Ooh that page is a little hard to understand for me, but i take your word for it. Thank you! $\endgroup$ Commented Feb 26, 2021 at 14:39
  • $\begingroup$ Yeah, no issues, I just meant that hydration is what imparts overall stability. $\endgroup$
    – PV.
    Commented Feb 26, 2021 at 14:45

1 Answer 1


The stability of an ion in an aqueous medium is determined by the tendency of attraction between the ion and the water molecules termed as hydration enthalpy. It, in turn, depends on the charge on the ion and its size.

Smaller the ion greater the hydration power of the ion. It is because when the ion is small the distance between its centre and the molecule that solvates it is less hence providing a stronger attraction, thereby releasing more energy attributing to stability. The example of this fact is provided by Cu2+ which has a smaller cationic radius due to a stronger hold of the nucleus on the remaining 27 electrons after the loss of two as compared to Cu+ where only one electron is lost and the hold of the nucleus is less. The stability gained by energy loss in hydration is more stabilising than the destabilising effect of the removal of 2 electrons.

Also, as mentioned earlier, the greater the charge on the ion greater is its tendency to attract and keep the water molecules solvated to it. Cu2+ having a greater charge has a greater tendency of hydration than Cu+.


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