* Reactivity and the Periodic Table: Reactivity of metals generally increases as you move down and to the left on the periodic table. Sodium is located in Group 1 (alkali metals), while copper is in Group 11 (transition metals). This means sodium is higher up and further to the left, making it more reactive.

* Electron Configuration: Sodium has only one valence electron, which it readily loses to achieve a stable electron configuration. Copper, on the other hand, has multiple valence electrons, making it more difficult to lose them.

* Reaction with Water: Sodium reacts vigorously with water, producing hydrogen gas and a lot of heat. Copper doesn't react with water at all.

* Reaction with Oxygen: Sodium reacts quickly with oxygen in the air to form sodium oxide. Copper reacts with oxygen only in the presence of heat, forming copper oxide.

In summary, sodium is a highly reactive metal, while copper is relatively less reactive.