Explain why an atom has no overall charge.

An atom is comprised of protons, neutrons, and electrons. Protons have positive charge and the number of protons is dictated by the proton number, which is the same as the number of electrons, which have negative charge. Hence, as there are equal number of protons and electrons, the charges cancel out. Neutrons don't have charge so they do not contribute to the charge on the atom therefore the atom is neutral.