## Chemistry: The Central Science (13th Edition)

In the symbols $\frac{31}{16}X$ and $\frac{32}{16}X$ the bottom number, the atomic number, tells how many protons an element has and identifies the element. Thus, in order to find the element, look on the periodic table to find the element with an atomic number of 16. Upon doing this, it makes it clear that these are sulfur isotopes.