According to online resources oxyanions are named as

Per+element+ate eg. $\ce{ClO4-}$

Element+ate eg. $\ce{ClO3-}$

Element+ite eg. $\ce{ClO2-}$

Hypo+element+ite eg. $\ce{ClO-}$

1-If I see an oxyanion should I assume that other oxyanions of same element also exists? e.g. $\ce{BO3^{3-}}$ is borate. Do Borite, hypoborite, perborite also exist?

2- How can I write formula of an oxyanion from a given name? For example Carbonate =$\ce{CO3^{2-}}$, while Sulphite =$\ce{SO3^{2-}}$. Both have same number of oxygen atoms and same oxidation state of C and S but names are different. How to know how many oxygens would be in an oxyanion?


4 Answers 4


This is about nomenclature, and when a nomenclature is established (a convened standard), this best not only considers compounds already isolated from a sample in nature, or once synthesized in a lab, but has rules powerful enough to accommodate new chemical elements and compounds. And IUPAC's rules, because systematic names are based on the chemical composition and structure of a compound, allow to name hypothetical compounds still unknown to literature.

On the other hand, chemical nomenclature equally is subject to change, and continues to evolve gradually; all while common names based on early assumptions (on occasion today known as wrong) tend to stick.

Chemistry.se has a page resources with a section about contemporary chemical nomenclature. IUPAC's freely available .pdf of the Red Book about inorganic chemistry is among the links, rule IR 8-3 states:

"Table IR-8.1 also includes anions from the neutral oxoacides by successive dehydroniation. Many of these anions also have common names that are still acceptable, in some cases despite the fact that there are now otherwise abandoned (e.g. nitrate/nitrite and perchlorate/chlorate/chlorite/hypochlorite)."

To quote (edition 2005, p. 131):

(Hill) formula acceptable name systematic additive name
$\ce{[ClO4]^-}$ perchlorate tetraoxidochlorate(1-)
$\ce{[ClO3]-}$ chlorate trioxidochlorate(1-)
$\ce{[ClO2]-}$ chlorite dioxidochlorate(1-)
$\ce{[OCl]-}$ hypochlorite chloridooxygenate(1-)

And similar about the analogues with bromine; tetraoxidobromate, trioxidobromate, dioxidobromate, bromidooxygenate. This contrasts to ions of borates which, in the solid state, tend to yield are larger, interconnected units. Hence a modern systematic nomenclature accounting for this diversity is more complex. (For a glimpse about e.g., meta, ortho, perborates and their structures, visit e.g., Wikipedia's entry page here).

  • 1
    $\begingroup$ I've taken the liberty to 'convert' your MD Table so that it renders correctly. Not that big of a change. I recommend bring such things up on meta if you have questions about it. I guess there is already something about it there… I would need to look, too. Btw. I think the "LaTeX table" was alright, too. I think in general the MD Table works better though. $\endgroup$ Feb 15, 2023 at 0:01
  • $\begingroup$ Thank you very much for the helpful edit. The "LaTeX table" already followed a pattern explicitly posted as example on chemistry.meta (here), however I agree, the markup with .md is lighter (hence equally easier to read by the non-initiated) than the one with .tex. $\endgroup$
    – Buttonwood
    Feb 15, 2023 at 7:17
  • $\begingroup$ Systematic additive names are much helpful. These should be used to avoid confusion. Thank you for valuable information. $\endgroup$
    – Level1
    Feb 15, 2023 at 9:19

The following rules were decided in the $19$th century.

When there is only one oxyanion containing $1$ element X and "some" Oxygen atoms, this anion is called "X-ate", whatever the number of O atoms and the charge of the anion. Example : As the only anion containing $\ce{1 C}$ and "some" O atoms is $\ce{CO3^{2-}}$, this anion is called carbonate. Important point is that there is no relation between the suffix and the number of O atoms.

If two anions are known differing only by the number of Oxygen atoms, the preceding rule is applied by the most oxygenated ion. The other anion is called X-ite. Example : In the 19th century, two anions were known containing $1$ N and "some" O atoms. They are $\ce{NO3^-}$ and $\ce{NO2^-}$. The first one is called nitrate, and the second nitrite. Here too, there is no relation between the choice of the suffix -ate or -ite and the number of O atoms. -ate means maximum, and -ite means minimum. This is the most important point of this nomenclature.

If four anions are known differing by the number of Oxygen atoms, the preceding rule is applied by the two central anions. The two extremes are called by adding a prefix "hypo" in front of X-ite for the lowest amount of O atoms. The prefix is "per" before X-ate for the largest amount of O atoms. Example : Anions containing chlorine, displayed in the original request.

If only three anions are known differing by the number of Oxygen atoms, one tries to "invent" a fourth ion, in order to apply the preceding rule.

  • $\begingroup$ Bromites are known and I don't see why you waste time on "questions" like this one. $\endgroup$
    – Mithoron
    Feb 14, 2023 at 20:48
  • $\begingroup$ Perbromate was only made in 1968... $\endgroup$
    – Mithoron
    Feb 14, 2023 at 21:40
  • $\begingroup$ Many people don't understand chemistry because of such doubts and quit reading. I believe every answer will be appreciated by many like me. $\endgroup$
    – Level1
    Feb 15, 2023 at 9:08

Let me illustrate through an example...

$\ce{HClO}$ is called hypochlorous acid, the corresponding acidic radical $\ce{ClO-}$ is called hypochlorite ion. In both of these, oxidation number (O.N.) of $\ce{Cl}$ is +1.

$\ce{HClO2}$ : Chlorous acid; $\ce{ClO2-}$ : Chlorite ion; O.N. : +3

$\ce{HClO3}$ : Chloric acid; $\ce{ClO3-}$ : Chlorate ion; O.N. : +5

$\ce{HClO4}$ : Perchloric acid; $\ce{ClO4-}$ : Perchlorate ion; O.N. : +7

As you can observe, "hypo-...-ite" refers to the lowest oxidation state of the element (in oxyacid form), "...-ite" is used for the next oxidation state, "-ate" for the next and "per-...-ate" for the highest oxidation state.

So basically the existence of the "-ate" and the "-ite" forms totally depends upon how many oxidation states that element can show in oxyacid (or oxyanion) form.

Also, it is to be noted that if an element exhibits two oxidation states in its oxyanions, then we generally prefer to name the ions as "-ite" and "-ate" corresponding to the lower and higher oxidation states respectively.

I hope this helps. Please feel free to correct me if I have erred anywhere.

  1. Not necessarily. For example, in the case of the halo-oxyanions (like the ones you mentioned), all of the different ones exist. This is not necessarily the case. For example, in the nitrogen oxyanions, there are only nitrate ($\ce{NO3-}$) and nitrite ($\ce{NO2-}$).

  2. The -ate/-ite naming system is not standardized. The only way (that I'm aware of) to know them is to memorize them. For example, sulfate is $\ce{SO4^{2-}}$ while nitrate is $\ce{NO3-}$.


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