[Abder-Rahman]

In an example about calculating the oxidations number for the atoms in: NaHSO₄

When solved, it considered "Na" as a monoatomic ions and based on that it ON was +1.

But, why don't we consider "S" for example a monoatomic ion and thus calculate the ON for "Na" based on the ON values of the other elements.

And, yes, the result for "S" and "Na" will differ in this case.

So, how do we recognize between monoatomic ions that their ON will equal its charge and between atoms that we cannot find its ON except after knowing the ON for all the other atoms, like "Na" and "S" in this example?

Thanks.

[opti384]

HSO₄ ^2- it self works as an ion.

[rabolisk]

We don't consider S a monatomic ion, because it doesn't exist as one in solution. NaHSO₄ is a salt, where the cation is is Na⁺, and the anion is HSO₄^-.

You should also recognize some useful tips on finding oxidation numbers.

1. Free atoms (0 charge) are 0
2. The overall charge of a compound equals the sum of oxidation states of its constituent elements.
3. Fluorine is -1 if it is bonded to anything other than itself, always.
4. Hydrogen is always +1 or -1 if it is bonded to anything other than itself.
5. Oxygen is almost always -2 if it is bonded to anything other than itself. Peroxides and superoxides are exceptions.
6. Group I elements are +1, and Group II elements are +2.

[opti384]

*HSO₄ ^-