Chemistry Disproportionation question AS

The systematic name for NaClO Is sodium CHlorate (I). Other chlorate compounds exist, such as NaClO3.

Give the systematic name for NaClO3.

Sodium chlorate (V)

When heated NaClO3 disproportionates as shown in the equation below.

4NaClO3 --> 3NaClO4 + NaCl

Using oxidation numbers, explain why this is a disproportionation reaction.

Now to be honest, i knew i was wrong in this question but i managed to get 2/3 marks from it, as the mark scheme allowed wrong oxidation numbers, as long as it showed some sense that Cl is both oxidised and reduced.

Now what i don't understand is that the markscheme says that chlorine has been oxidised from +5 to +7 and reduced from +5 to -1.

Why can chlorine change the oxidation number so drastically like in NaClO3 it's +5,
if oxygen is-2 then couldnt it be +3 and Na also be +3, why does Na always stay +1, and is this just an exception to the rule or does this apply to every chlorine element in every compound?

Also, for the systematic name of NaClO3, wouldnt the overall charge of the compound be -1? Why is the overall charge 0 in the second question?

Thank you.

Are you an AS or A2 level student? Either way, you will have figured out that Na's electron configuration is 1s², 2s², 2p⁶, 3s¹.

Now, Na⁺, which is the most stable sodium ion is [1s², 2s², 2p⁶]⁺. This means that it has a full outer shell of electrons (so it's more stable).

Therefore, sodium only forms Na⁺ ions.

With regards to NaClO₃'s OS of 0, Na (as has been discussed above) is +1, and Oxygen is (pretty much) always -2. Therefore, chlorine is +5 (which is true, since this is Sodium chlorate (V)), and therefore the overall oxidation state of the compound is 0.

I understand that, but what i'm asking is why must sodium become stable, Cl- would make chlorine more stable no? Why is sodium in preference?

Sorry, I don't really understand what you're trying to ask

the reaction would be disproportionation as the chlorine is both reducing from 5 to -1 and oxidising from 5 to 7.For a compound that has no overall charge like NaClO3, the oxidation number would have to be 0, not -1, so the oxidation number of chlorine here is 5 giving it the systematic name of sodium chlorate (V)