# When to use -ate and -ite for naming oxyanions?

I'm now learning about nomenclature. In particular, oxyanions.

Basically, when you have an anion that is a combination of a non-metal with oxygen.

According to my book:

It ends with -ate for the most common oxyanions of the element. It ends with -ite for the oxyanions that have the same charge but with one less atom of oxygen.

Example:

$\ce{NO_3^- \implies}$ Nitrate

$\ce{NO_2^- \implies}$ Nitrite

Ok, if you give me an oxyanion that ends with -ate, I know that I can simply remove one oxygen atom and I will get the -ite.

But, what I don't understand is how does the book know that $\ce{NO_3^-}$ is Nitrate: how does the book know that $\ce{NO_3^-}$ is "the most common oxyanion for the element". How does it know that a charge of $-1$ and $3$ oxygen atoms create "the most common" Nitrogen oxyanion?

In other words, what does it even mean by "most common"?

• I'm actually not sure about this, at first I thought it would be something to do with the group oxidation number since nitrate, sulfate and phosphate all feature the central ion in its group oxidation number. But chlorate ($\ce{ClO3^-}$) begs to differ. I guess, as with lots of chemical nomenclature, it may just be due to "historical reasons". Hope someone else can give a better answer. – orthocresol Jun 16 '15 at 10:26
• @orthocresol your right but there's also per- prefix - en.wikipedia.org/wiki/Oxyanion – Mithoron Jun 16 '15 at 12:56

"Most common" means the forms most frequently encountered in the entire scope of chemistry, which I'm pretty sure corresponds loosely to the most thermodynamically stable oxidation state. It is not always the case that the '-ate' ion is the most stable, however—as an example, see the links for chlorine below).

A detailed answer necessitates noting that the nomenclature extends beyond just '-ate' and '-ite'. Most p-block elements that form oxo-anions form a whole series of them, each with the central atom in an oxidation state two away from each neighbor. For all elements except the lightest ($\ce{C}$ and $\ce{N}$) and heaviest ($\ce{As}$, $\ce{Se}$, $\ce{Te}$, etc.) , usually the series is considered to contain four members, though it is not guaranteed that all are stable or able to be characterized (e.g., "bromite" and "hyposulfite").

As noted in the comments to another answer, in addition to the '-ite' and '-ate' suffixes, there are also the 'hypo-' and 'per-' prefixes, where 'hypo-' only is used with '-ite', and 'per-' is only used with '-ate'. These four combinations are used to span the series of oxo-anions for each element:

For carbon, 'carbonate' was given preference, per the 'most common' rubric, as the only known oxo-anion. For nitrogen, the use of the prefixes was avoided, for what I assume was the sake of simplicity. (I would argue that nitrate and nitrite are both common enough in the natural world that without such a deciding factor there would have been stiff competition for the '-ate' suffix.)

Possible irregularities in structure within a series include peroxo-anions at high numbers of bound oxygens (e.g., I believe persulfate and "perphosphate" are both peroxo species) and variable numbers of bound oxygens for a given oxidation state in anions of heavier elements (e.g., metaperiodate, $\ce{IO4-}$, versus orthoperiodate, $\ce{IO6^{5-}}$, both of which contain heptavalent iodine). As well, there is the possibility for other, non-oxo-anion compounds of the central atoms with oxygen such as chlorine dioxide, $\ce{ClO2}$; nitrogen dioxide, $\ce{NO2}$; sulfur dioxide, $\ce{SO2}$, and trioxide, $\ce{SO3}$; and (of course) carbon dioxide, $\ce{CO2}$.

You can find references to oxo-anions of arsenic, selenium, antimony, and tellurium also (links are to the '-ates'), but to my mind, these tend to edge more toward the behavior of oxo-anion-forming metals, which either only have a single appreciably stable oxo-anion (chromate, molybdate, tungstate, etc.), or break this (hypo-)-ite/(per-)-ate paradigm pretty badly (see, e.g., permanganate, $\ce{MnO4-}$, versus manganate, $\ce{MnO4^{2-}}$).

If you really want to blow your mind, take a look at the polymeric oxo-anions like polyphosphate; or at the at-present theoretical-only orthocarbonate; or at iron, for which apparently all three of the known oxo-anions are referred to as 'ferrate'.

Historical naming conventions dictate that the "-ate" suffix refers to the group containing the cation with a higher oxidation state than that in the corresponding group designated with the "-ite" suffix.

In the case of nitrate, nitrogen carries a +5 charge; in nitrite, nitrogen is a +3. For chlorate, chlorine is +5; in chlorite, it's +3. And so on.

• However, there is also the prefix per- which denotes an oxidation state higher than just an -ate. – bon Jun 18 '15 at 20:44
• And also 'hypo-', which denotes an oxidation state lower than '-ite'. E.g., hypochlorite, $\ce{ClO-}$. – hBy2Py Jun 18 '15 at 21:11
• @bon I was taught that "per-" is an abbreviated form of "hyper-", which pairs nicely with "hypo-". – Jason Patterson Jun 18 '15 at 21:14
• @JasonPatterson This seems quite likely. – bon Jun 18 '15 at 21:15
• The "per-" prefix is due to Thomas Thompson (and is not an abbreviation for "hyper-" but rather denotes the highest oxide). See M.P. Crosland's excellent text Historical Studies in the Language of Chemistry. – Todd Minehardt Jun 18 '15 at 23:44