How many electrons does the copper ion gain or lose when it forms the compound CuCl2?

Copper(II) chloride, CuCl2, does not actually form “ionic” bonds. A common misconception often propagated by well meaning teachers who may not really “get it” is that a metal and a nonmetal form an ionic bond.

For CuCl2, that is simply not the case. Copper-chlorine bonds have about 33% ionic character (67% covalent character). Copper(II) chloride is a polymer.

There are no 100% ionic bonds, and a few 100% covalent bonds. “Ionic” and “covalent” are the hypothetical ideal bonds at either end of the bonding continuum. Real bonds lie along the continuum and have characteristics of both of the ideal bonds.