Why does chlorate seem to break the pattern of polyatomic ions?

[FysicsPhorums]

Hi, I was reviewing the polyatomic ions, and on the third row of the periodic table they seemed to follow a pattern going from left to right on the periodic table. For example:
Silicate = SiO₄^4-; phosphate = PO₄^3-; sulfate = SO₄^2-

For row 3 on the periodic table, it looks like each polyatomic has 4 oxygens, the charge increases by one as one moves to the right along the periodic table, and I think the oxidation numbers of the non-oxygen elements goes +4, +5, +6, respectively. However, chlorate is ClO₃^-, which seems to break the pattern, since it has only 3 oxygens instead of 4, and the oxidation number on chlorine of +5, instead of +7.

Is there any reason chlorate seems to "break" the pattern of the polyatomic ions so far, and any reason why for naming purposes, ClO₃^- is chlorate, instead of chlorite (like PO₃^3- is phosphite, for example)?

Thanks!

 

[samblohm]

Well actually there is a Perchlorate ion that is ClO4 that has a negative 1 charge so the pattern isn't broken. Chlorine is just very flexible in a sense because it can have anywhere between 1-4 oxygen atoms and still have a minus 1 charge.
ClO is Hypochlorite
ClO2 is Chlorite
ClO3 is Chlorate
ClO4 is Perchlorate
The naming has to do with the other form of the polyatomic ion can be.

 

[FysicsPhorums]

So is ClO₄^- called perchlorate simply because there is no ClO₅^-? I understand how perchlorate would be named relative to chlorate, and so on, but I'm trying to figure out why the naming for the other polyatomic ions I mentioned had 4 oxygens for the "ate" names. But for chlorate, the form with 3 oxygens carries the "ate" name. Thanks again for the help!

 

[samblohm]

In general, the most common oxyanion for an element will end in ate. You will find many trends in the periodic table, but you will also find many exceptions.

Some examples I can think of for ate's that have 3 oxygens are nitrate, bromate, iodate, carbonate (although that has a minus 2 charge)

And I don't think there is an element that has 5 different oxyanions.

 

[LudusRex]

I can provide an explanation for why chlorate may seem to break the pattern of polyatomic ions. First, it is important to note that the patterns observed in polyatomic ions are not strict rules, but rather general trends that can be observed. There are always exceptions and variations within chemical compounds.

One possible reason for the difference in the number of oxygen atoms in chlorate compared to the other polyatomic ions is due to the electronegativity of the elements involved. Oxygen is more electronegative than chlorine, meaning it has a stronger attraction for electrons. This can result in a more stable compound with fewer oxygen atoms bonded to the central chlorine atom.

Additionally, the naming of polyatomic ions is based on historical and traditional naming conventions, rather than strict rules. The name "chlorate" has been used for a long time and has become the accepted name for this particular polyatomic ion. While it may not follow the same naming pattern as other polyatomic ions, it is important to remember that the name of a compound does not necessarily reflect its chemical properties.

In conclusion, while chlorate may seem to break the pattern of polyatomic ions, there are valid scientific reasons for its structure and naming. As scientists, we must always be open to exceptions and variations in chemical compounds and continue to explore and understand their properties.