Why Cu looses 2 electrons to become stable instead of gaining one electron to fill its 4s2 3d10 configuration?

Cu has 4s1 3d10 configuration so why it does not gain 1 electron and complete its suborbital. Why it looses its 2 electrons to become Cu++ which is more stable. Why?




Copper can gain 1 electron to become Cu-. 


Copper has an electron affinity of 1.236 eV, so Cu- is stable to electron loss by 1.236 eV.


See also "The Dissocationi Energy and Heat of Formation
of the Molecule NaCu" Z. Naturforsch. 28a, 316-317 which says:



> 
> But unlike as for NaAg a noticable ionic contribution
>  to the bonding is observed for NaCu
> 
> 
> 


Also there is [Resonant two-photon ionization spectroscopy of LiCu](http://chem.utah.edu/_documents/faculty/morse/87.pdf) :



> 
> The unusual shape of this curve is thought to derive from avoided
>  crossings between the $\ce{Li^+Cu^-}$ ion pair state and covalent states, with the $\ce{Li^+Cu^-}$ ion pair state
>  ultimately correlating to the ground electronic state of the molecule.
> 
> 
> 


So if Cu is to make a compound with an electronegative element, Cu should lose electrons, but with an electropositive element it can gain an electron.


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