Why does copper have one valence electron?

Answer 1

One electron is "borrowed" from the 4s shell to completely fill up the 3d shell. This is as the nearness of the energy between the two shells results in blurring of the order of electron selection. The same thing happens in chromium.

Answer 2

Copper can lose 1 electron (4s1) leaving a full 3d shell or lose an extra electron from the d shell (3d9). The 3d9 configuration is stabilised by the coordination sphere. Copper is a transition metal and these typically have multiple valencies.

Copper also has oxidation state of copper(III) and copper(IV) but these are much rarer.

Answer 3

Copper has one valence electron because it belongs to Group 11 of the Periodic Table, also known as the transition metals group. Transition metals tend to have one or two valence electrons, and in the case of copper, it has a single electron in its outermost shell, giving it a valency of +1 in most chemical reactions.

Answer 4

Copper often occurs in the 2+ oxidation state because it has 2 valence electrons that it can lose.

Copper can also occur in the 1+ oxidation state.