Heteroatom Heteroatom Hell In the nomenclature of Organic chemistry, a heteroatom (from Old Greek heteros, different, + atomos) is any Atom that is not Carbon or Hydrogen, typically, but not exclusively, Nitrogen, Oxygen, Sulfur, Phosphorus or Boron.

In the description of Protein structure, particularly in the now-deprecated Protein Data Bank file format, a heteroatom record (HETATM) describes an atom belonging to a small molecule cofactor rather than to part of a biopolymer chain.