You are correct that copper (Cu) is not an alkali metal or an alkaline earth metal. Copper belongs to Group 11 (Group IB) of the periodic table.
Copper has a unique electron configuration. It has two filled inner energy levels (1s² 2s² 2p⁶ 3s² 3p⁶), and the valence electron configuration is 4s¹ 3d¹⁰. While the valence electron is in the 4s orbital, due to the electron-electron repulsion within the atom, the 4s orbital has a slightly higher energy compared to the 3d orbitals.
When copper loses electrons, it tends to lose the 4s¹ electron first rather than the 3d¹⁰ electrons. Therefore, copper loses one valence electron to achieve a stable electron configuration of 3d¹⁰. After losing the electron, copper forms a Cu⁺ cation.
It's important to note that the reactivity of copper is relatively low compared to the alkali metals since the loss of a valence electron is energetically less favorable due to the proximity of the 3d electrons to the nucleus. However, copper still exhibits typical metallic properties due to the presence of delocalized electrons in the metallic lattice, which are contributed by the 3d and 4s orbitals.
In summary, copper loses one valence electron (4s¹) to form a Cu⁺ cation, but its reactivity is lower compared to alkali metals due to the influence of the electron-electron repulsion and the stability associated with the fully filled 3d subshell.