What is the charge of a single electron?
One electron holds a negative charge of 1-
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-.