To keep track of mass and charge in a nuclear change (reaction), we need to understand the notation that is utilized. The first thing to realize is that unlike chemistry where we look at atoms (nuclei + electrons), nuclear change often only looks at the nuclei and ignores the electrons.
Because the reactions deal with the nuclei, we need to know which specific isotopes we are dealing with for each element. Therefore we are always looking at specific isotopes (numbers of protons and neutrons) for any element rather than some natural mixture of isotopes.
First, a definition. nuclide: an atomic species specified by its number of protons and neutrons.
For example, a nuclide could be a Helium nucleus that has 2 protons and 2 neutrons. This nuclide would have a mass number of 4 (2 protons + 2 neutron = 4) and a charge of +2. This would be given the following symbol
\[\rm ^4_2He\]
For a nuclide, the charge is simply the number of protons. This is what defines what element it is. Any species with only two protons is "Helium". That is what makes helium helium. So in our symbolic representation the elements symbol and the charge number are redundant. However, it is very handy since generally it's hard to remember off the top of your head how many protons are in every element.
Any given element could have a large number of different isotopes. Generally they are referred to by their mass number and the element name (which is the charge number). So for example, we could have
\[\rm ^{197}_{\;79}Au\]
This would be called "gold-197". It is gold (Au) since it has 79 protons (the charge number of 79) and it has 118 neutrons (197 - 79 = 118).
\[\rm ^{195}_{\;79}Au\]
"gold-195" has 79 protons (or it wouldn't be gold) but it has 116 neutrons.