List 4 types of information that are given in each box of the periodic table:

1) the element symbol, and thus name. For example, H is hydrogen, C is carbon and Fe is iron.

 2) The atomic number, which is equal to the number of protons in the nucleus.

 3) Since each proton has a +1 charge, you can also figure out the number of -1 electrons in the neutral atom.

 4) The atomic mass, in atomic mass units, which is an average of 1 or more isotopes of the element.  

The number of atoms of each element on each side has to be the same for the Law of Conservation of Mass to apply.