118 elements
Actually, there are 117 elements on the periodic table. But, they couldn't make element number 117 so it's 1-116 and then 118.
118
There may be many elements that aren't on the periodic table, but it is because if they're not on it, that means they haven't been discovered. The periodic table contains only discovered elements, so...
There are 115 elements in the periodic table as there are 3 spaces left for undiscovered elements.