how do u figure out charges of polyatomic ions?

Question

help!

Answer 1

A few tips: if you need to solve for a non-common poly, use oxidation numbers, ie. if given CO3 with no other info then using ox. numbers will tell you that the charge must be -2 since C is +4 and each O is -2.

If you need to memorize a bunch of polys, then organize them: notice that nitrite and nitrate are both -1, and that nitrite is NO2 and nitrate is NO3. It is always true that -ites have one fewer O than -ates, and that the polys of the same type always have the same charge. Memorize either the -ates OR the -ites and learn the rule about one fewer O. Then you will want to use the prefixes hypo- and per-, such as in hypochlorite->chlorite->
chlorate->perchlorate and notice how hypo is one fewer O than -ite, and per- is one more O than -ate.

Hope that makes sense.

Answer 2

Well, if you are dealing with the more common ones such as nitrate (NO3-) or perchlorate (ClO4-), you simply remember them. (In a test situation when asked to write the formulas with the proper charges, your are not gonna have the time to go through and figure out the charges properly.)

Now, lets say you don't know the charges, but you know what the polyatomic ion is AND its in a formula. In that case, you simply balance the charge of the cation and anion so that the total charge is zero.

For example, what is the charge of nitrate in sodium nitrate (NaNO3)? We know the compound charge is zero and we know that the charge on sodium MUST be zero. Therefore, in order insure charge nuetrality the charge on nitrate MUST be zero.

Answer 3

Ya gotta know the charges of the atoms involved and some simple rules, like oxygen is almost always -2 and Group 1 and 2 cations are almost always +1 and +2, respectively.

Answer 4

memorization. i know it sucks but thats the only way.