What is the number placed below an elements symbol in a chemical formula?

1 Answer
Apr 2, 2017

Answer:

Such numbers relate to the #"molecularity"#; the molecular composition of the element.........

Explanation:

Elemental oxygen, nitrogen, fluorine, and chlorine, IN FACT ALL THE ELEMENTAL GASES EXCEPT FOR the #"Noble Gases"# are #"BIMOLECULAR"# under standard condtions; i.e. #H_2#, #O_2#, #N_2#, #F_2#, and #Cl_2#. That is the standard elemental state is a diatom, #H-H#, #O=O#, #N-=N# etc............This must simply be known, and the usual problems, even at A level, will ASSUME this knowledge.

Sometimes, we represent sulfur as #S_8#. All of the halogens are #X_2#, but only the two are gases under standard conditions. What about #Br_2#, and #I_2#?

Of course, in compounds, i.e. #LiNO_3#, #HClO_4#, the subscript refers to the number of oxygen atoms in a formula unit. Capisce? If this does not address the question you have asked, fire away, and someone will help you.