It also tells us that chlorine has 18 neutrons (35 - 17) and, as the number of electrons and protons are equal in a neutral atom, chlorine also has 17 electrons. The relative mass of a nucleus is ...

When building an atom, pay close attention to the particles' electrical charges. Protons have a charge of +1. Electrons have a charge of -1. Neutrons are neutral, as its name implies. A stable ...