As of 2014, there are 118 elements on the periodic chart.91 of these are generally in the list of naturally occurring elements, with atomic numbers 1 to 92. Technetium, element number 43, is radioactive with a very short half-life, so scientists initially did not believe it occurred naturally; such beliefs have since been refuted. About.com reports there are 98 naturally occurring elements.
The first synthesis and testing of elements 93 to 98 occurred at Berkley Radiation Laboratories at the University of California. Later discoveries found these elements in radioactive fallout. They also exist in samples of uranium-rich pitchblende, although in very small quantities.
Elements above atomic number 98 are all radioactive elements. As of 2014, they are only known to exist in atomic accelerators in which scientists collide two elements to create a new element with a larger nucleus. The half-life of such elements is so short that scientists have evidence they exist, but are unable to isolate them for further study.
Dmitri Mendeleev developed the first periodic table. While similar to the one in use today, Mendeleev's 1869 table included many gaps and question marks for elements unknown at the time. Using this table and predicting the behavior of such groups of elements helped scientists discover the elements that filled the gaps.