Electrons have single negative charges. What does this mean?

In an atom, the protons hold a positive charge, the neutrons a neutral charge and the electrons a negative charge.

So long as it is not an ion, the charge of this atom will always be 0 overall, with the same amount of protons as electrons. So one singular electron with no proton to balance it out must have a negative charge equivalent to the number of electrons more than protons. Thus the overall charge must be 1-.

Copper, silver, aluminum, cobalt, chromium, mercury