In D&D there are 4 elemental planes and matter is made of the four classical elements differentially permeated by positive (life) and negative (death) energy, and with the magical weave thrown in.
The four elements were briefly supplanted by phlogiston, the essence of combistion, which along with dephlogistonated residue made all matter. In Spelljammer 'phlogiston' has terrible usage as the interstellar medium, which in all likelihood is from someone's laziness at not checking their words as they meant æther.
Modern atomic elements do not explicitly feature, except in Order of the Stick and in games that are higher than progress level 5 (Alternity/D20 modern term).
Radiation features in Pathfinder Technology guide, which means that nuclear physics is possible. This means that if the minor conjuration were still around he could have summoned a critical amount of a fissile material, which combined with poison and fire immunity would be unspeakably awesome.
Also, atomic theory elements would mean different planar realms. It would not be recommendable visiting the trans-uranic planar realms. But the gold plane would probably make the GM cry the most.