[illuminatus104]

Hello

I'm working on naming compounds and would like to know if there is a way to figure out the charge of a "common polyatomic ion". In the text book, there are a few polyatomic ions that we were told to memorize. Do I have to memorize the charges also, or is there a way to figure out the charge? For example


Na2SeO4

So I know that the sodium in this polyatomic ion has a charge of +2, or +1 for each. How do I know that selenate has a charge of 2-? Or does SeO4 have to neutralize the charge of the sodium, so if I know the sodium charge, I know the selenate charge.

I just began learning this, so correct me if I'm using the wrong words to describe something.


Ah, I think asking the question helped me answer it myself. A polyatomic ion must be stable, meaning that the charges are going to neutralize each other like I suspected. So if sodium has a charge of 1+ per atom?, so 2+ for this problem, then the polyatomic ion SeO4 will have a charge of 2-. Is this the case?

[Borek]

Several ways to skin that cat.

You can memorize.

Na is always +1, so in Na₂XO₄ there is no other possibility than XO₄^2-.

Finally, in periodic table is above sulfur, which is a strong indication its chemistry should be to some extent similar. That means you can expect selenic acid to be similar to sulfuric acid - so H₂SeO₄, just like H₂SO₄.

[illuminatus104]

Thank you borek, I understand now.