Within an organic compound, which by definition always contains carbon (C) and hydrogen (H), a heteroatom is any atom other than carbon or hydrogen, such as oxygen (O), nitrogen (N), sulfur (S) or a halogen. Heteroatoms matter because they introduce polarity and lone pairs into an otherwise unreactive carbon–hydrogen framework, and so they are usually the site at which a molecule reacts. For example, the oxygen in an alcohol and the nitrogen in an amine are both heteroatoms.

在有机化合物中(其定义上总含有碳(C)和氢(H)),杂原子是指除碳和氢以外的任何原子,如氧(O)、氮(N)、硫(S)或卤素。杂原子之所以重要,是因为它们把极性和孤对电子引入原本不活泼的碳氢骨架中,因而通常正是分子发生反应的部位。例如,醇中的氧和胺中的氮都是杂原子。