An atom contains a proton, electron and neutron as subatomic particles. The number of protons, which is the positively charged particle (+) is always equal to the number of electrons, which is the negatively charged particle (-) in A NEUTRALLY CHARGED ATOM i.e. no charge.
However, a decrease or increase in charge is dependent on the number of electrons and protons in that atom. Sulfur atom has an electron number of 16 in its neutral atom, however, when it gains one more electron to become 17, it means that the charge has become -1 because the charge = number of protons - number of electrons i.e. 16 - 17 = -1.
