What is the rarest element on the periodic table?
There are a number of elements on the periodic table listed as Synthetic Elements. They are highly unstable, and thus only exist in laboratory conditions for a short period of time. These would be the ones listed on the bottom of the periodic table with only the atomic mass number listed in parenthesis. Some, for example, Technetium was initially synthesized, but later discovered as a very rare naturally occurring substance on earth. See notes on Wikipedia: http://en.wikipedia.org/wiki/Synthetic_element However, one of the rarest of all elements is not actually on the periodic table. Antimatter in the form of Positrons (anti-electrons) and anti-protons (essentially anti-hydrogen) has been synthesized in the laboratory, but it is highly reactive with all “normal matter”, and thus can only be maintained for a very short period of time. It is believed that antimatter reactions have been observed in astronomy, but it is unknown whether there exist any antimatter stars, solar systems, and g
