The total number of isotopes of Silicon is 9, with mass number varying from 25 to 33, but, when we talk about stable isotopes, we can have 3, Silicon-28, Silicon-29 and Silicon-30, the 28 is the most abundant. Assuming all three isotopes are neutral, the number of protons and electrons will be the same for all 3 isotopes, p and e = 14, the number of neutrons will change, because the atomic mass of an atom is the sum of the number of protons and number of neutrons. In Silicon-28 we have 14 neutrons and 14 protons and 14 electrons, In Silicon-29, 15 neutrons, 14 protons and 14 electrons, and in Silicon-30, 16 neutrons, 14 protons and 14 electrons.