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 ...

For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus ...

Because the mass of a proton is equivalent to a neutron, the relative mass of an atom is the same as its nucleon (mass) number. Neutrons have no charge. Protons are positively charged. So the ...