There are two main forms of copper oxide:

* Copper(I) oxide (Cu₂O), also called cuprous oxide, is a reddish-brown solid.

* Copper(II) oxide (CuO), also called cupric oxide, is a black solid.

The specific copper oxide formed depends on the reaction conditions, like the temperature and the amount of oxygen present.

Here's a simplified equation for the reaction:

2Cu + O₂ → 2CuO

This equation shows that two copper atoms react with one oxygen molecule to produce two molecules of copper(II) oxide.