What are the electronic configurations of copper metal, and copper ions?

The abridged electronic configuration of copper is, #[Ar]4s^(1)3d^(10)#. #"Cuprous ion"#, #Cu^+#, is well-known. However #"cupric ion"#, #Cu^(2+)#, has a configuration of #[Ar]3d^(9)#, and can properly be regarded as a transition metal, with a partly filled #"d-shell"#. But theory follows experiment, not vice versa.

The electron configuration of Copper is

# 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^9 #

When copper has a +1 charge one of the 4s electrons is moved to a slightly higher energy state of the 3d. When one of the 4s electrons is moved to the 3d sub orbitals there are 10 3d electrons completely filling the 3d sub orbitals, making it more stable. as the 3d orbitals sink down to the third energy level.

In a similar manner the # 3d^9# electrons can sink down into the third energy level even though it is not filled. When the 3d orbitals are no longer valance electrons by being in the outmost shell, the valance electrons are the two 4s electrons. These two electrons can be used in bonding creating a +2 charge.

Copper becomes a + 2 ion by losing both of the 4s electrons. Losing the two 4s electrons makes copper more stable.