Well, there are those elements that have only been observed when created under laboratory conditions, and there are elements that are very rarely found in nature, but generally are only made in a laboratory or a reactor. read more
All of the elements found on the periodic table above Uranium, element 92, are man-made. Stars form heavier elements than Hydrogen and Helium by nuclear fusion. Uranium is the upper limit for an element that is stable enough to detect. read more
The first element discovered through synthesis was technetium—its discovery being definitely confirmed in 1936. This discovery filled a gap in the periodic table, and the fact that no stable isotopes of technetium exist explains its natural absence on Earth (and the gap). read more