# What is the structural formula of alkali hypohalite: MOX or MXO?

Recently I came across this question and in the comment section, there was an argument regarding the formula of sodium hypoiodite which kept me wandering: what is the actual formula of alkali hypohalite: MOX or MXO?

There seems to be an inconsistency in the formula, somewhere it is written MOX and in other places, it is written MXO. In the wikipedia article of sodium hypochlorite, sometimes it is written $\ce{NaOCl}$ and at sometimes it is written $\ce{NaClO}$. This is what was written in the brief:-

I think the formula of alkali hypohalite should be MOX because since the negative charge bears over the oxygen atom, it accepts the electron coming from the alkali metal ion and forms a duplet and thus forming ionic bond.

Is my assumption correct? What is the correct formula of alikali hypohalite?

I felt tempted to close this as a duplicate of the sodium acetate notation question, because of my answer there, but the question in itself does not ask the same thing, so I’ll just rewrite the relevant parts of my answer.

In short, there is no correct formula. Depending on which point you want to bring across, you can use either, and depending on the context, $\ce{ClNaO}$ may also be acceptable.

Structually, you are correct with your assumption; the oxygen bears the negative charge. But that doesn’t include any implication that the formula should be written that way; compare $\ce{SO4^2-}$ where the charge is also on the oxygen atoms and yet they come last.

In fact, that leads us to our first clue. By convention, oxygen atoms are typically written last; compare $\ce{ClO3- , ClO4- , BrO3-}$ and others. You could probably explain that with electronegativity, the convention being that electronegative elements come last. This assumption argues for $\ce{NaClO}$.

On the other hand, the corresponding acid $\ce{HOCl}$ is often understood as derived from water $\ce{HOH}$, replacing a hydrogen with a chlorine atom. From this starting point, it makes sense to write $\ce{NaOCl}$, because then you replaced the other hydrogen; this time with sodium. It also includes a resemblance to $\ce{NaOH}$.

Both ways can thus be supported by the reasons given above. In practice, I think I have always seen the substance being referred to as $\ce{NaOCl}$ but I could simply have ignored the occurances of $\ce{NaClO}$.

• But sir, you can't write ClNaO because the compound is made up of Na+ and [OCl]- ions. – Nilay Ghosh Jun 13 '16 at 4:43
• $\ce{ClNaO}$ is the Beilstein-type lookup formula and accepted whereever alphabetic ordering of elements is preferred/required. – Jan Jun 13 '16 at 12:58

Both formulae are correct. NaOX is correct structurally but preferred form is NaXO in correspondence with other series salts like Oxo-halate(III) NaXO2, Oxo-halate(V) NaXO3 and Oxo-halate(VII) NaXO4.

• I know both of them are correct but which one should be used? Explain with some reasoning. For ex- sodium chloride is also (incorrrectly) written as ClNa but that's not we use. – Nilay Ghosh Jun 12 '16 at 3:32