1) The International Union of Pure and Applied Chemistry announced there were more elements to the periodic table. So now there is 118 elements in the periodic table.
2) In 1869 by Russian chemist Dmitri Mendeleev. The first table had 59 elements. They're organized by how many protons are in each of it's atomic nucleus.
3) The reason we are unable to find naturally occurring examples is because the elements are extremely heavy and, therefore, decay quickly. To be considered for the periodic table the new element has to reproduced by another scientist working in a non-affiliated laboratory.
(Critical Thinking) The reason why it would be hard to create new elements is because they were unable to find naturally occurring examples because the elements are extremely heavy and, therefore, decay quickly.