chemistry question about names to formula

[mmapcpro]

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This is going to seem like a very elementary question.

Let's look at a phosphate ion for example.

1) How can I tell by looking at the name that it's an oxyanion? I know it's a polyatomic ion with phosporous.

2) Since it actually IS an oxyanion of phosphorous and oxygen, how do I know how many of each element are in the molecular formula?

My chemistry professor just told me to not worry about it because he's providing a chart of the cations and anions for the exam, but I'm trying to figure out what the concept is here that I'm missing. I want to take the DAT or MCAT next year, and I know we won't have any such charts to take the test with.

Can someone help me out?

 

[blankguy]

The way you can tell how many oxygens it has is by looking at the ending -ate and -ite. -ate has more oxygens than -ite
ex: NO2- nitrite and NO3- nitrate ion
SO3- sulfite and sulfate

note than nitrogen has 2 and 3 where as sulfur has 3 and 4.
How can you tell? Just memorize it. There is no way of getting around it but by memorizing.

Memorize the polyatomic ions and the number of oxygens.

The ions with just one element has -ide at the end.
ex: S2- sulfide


If you want I can list the polyatomic ions. Just pm me.

 

[mmapcpro]

I appreciate it, thanks...

I'm comfortable with the material...I was just trying to dig deeper and try to figure out how they were originally named.

My best idea thus far is that the ions and compounds were named as they were found, so the first oxyanion of an element would have been named with -ate, regardless of how many oxygens were attached to it. Then subsequent ions were named according to their relative oxidation states.

Basically, PO4 just happened to be found before PO3, and SO4 just happened to be found before SO3, and NO3 just happened to be found before NO2.

Does that sound alright? Obviously that means that you are 100% correct in that there is no way to deduce conceptually. It's just a matter of memorization and experience in using them.

It's not really an issue. I just have a hard time NOT looking for deeper understandings of concepts.