The reaction on the previous page was written using the notation introduced previously, with the subscript now representing the charge on a particle (rather than the number of protons in the nucleus), and the superscript giving the mass number, or approximate mass in amu.

A proton, which has a +1 charge and unit mass number, is written ; a neutron, which has no charge and unit mass, is ; and an electron, which has a - 1 charge and no negligible mass on this rough-counting scale, is . When a nuclear reaction such as this one is written and balanced properly, the total charge (subscripts) and the total mass number (superscripts) on the left must equal the total charge and mass on the right.