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

Question

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?

Answer 1

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 :

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.