The atomic number for copper is 29, which means that it contains 29 electrons. As electrons are negatively charged, they need an equal number of positively charged protons to balance them out, which means that copper also has 29 protons within its nucleus.
Although copper has 29 total electrons, it only has one electron in its outer shell. This makes copper highly reactive, as this lone electron can easily move from copper to another atom. In addition to the 29 protons, an atom of copper also contains 35 neutrons within its nucleus. The combination of the protons and neutrons gives copper an atomic mass of 63.55.