The transport of molecules at the plasma edge in tokamaks is discussed in order to compare how light impurities enter the plasma if they are released either in atomic or molecular form. Differences in their transport arise because of the dissimilarities between atomic and molecular reactions with the bulk of the plasma. It is found that re-cycling to the walls is more efficient for the light impurities released in molecular form, but, also, that a substantial fraction of those atoms which originate from molecules may penetrate further into the plasma.