mystery number is giving me a headache?

Question

ok if i need to find the formula for calcium phosphate the first step is to write the symbols:

CaPO

so after the Ca is the little number 2+ on top and after the PO is the little number 3- on top and 4 on the bottom...my question is, on this first step HOW DID THEY FOUND OUT THE 4 ON THE BOTTOM? i know how to get the other two #s, yet i cant seem to find how they get the 4...PLZ PLZ PLZ HELP ME!

yes, thank you i know the answer but how did they get the little 4 there on the bottom in that step that i typed above? where did it come from?????????

Answer 1

Phosphate is a polyatomic ion and is symbol is PO4 3+, so the calcium phosphate ion would be represented as Ca3(PO4)2...you can get the charge of the polyatomic ions by the charge of the nonmetal, in this case its Phosphorus

If the nonmetal touches Arsenic or is arsenic, then the subscript after the oxygen will be 4, if its an "ate," if its an "ite," it will have a XO3, if its an hypo----ite it will be a XO2, if it doesn't touch arsenic, for example, Chlorine, its "ate" would be a ClO3, its "ite" would be a ClO2 and so-forth