It does sound oxymoron-ish, but I'll take a stab. College was a long time ago, so be patient. I believe the man-made elements are the ones beyond element 92. They are all very rare, and many can only be made in very small quantities--like one atom at a time. I think the reason they're elements--which is to say they can't be broken down into simpler atoms--is because they are created by colliding big atoms like Uranium with atomic particles--pieces of atoms--not with other whole atoms. Once collided, they form a new species of atom altogether, which is whole and indivisible.
I am probably speaking directly out of my ass, but I thought I'd take a shot.
