How to find formula for compounds and naming?

Question

So how would you find the formula for sodium carbonate?

And how would you name this formula compound? Fe2O3

Answer 1

use the charges of the ions.

cancel out the charges by finding a common multiple of the + and - charges

Na is 1+

CO3 is 2-

common multiple is 2 (ignore the +/-), so you need 2 Na

Na2CO3

That is Iron(III) oxide

check these webpages on formulas and naming out

Kent

Answer 2

Sodium = Na+, Carbonate (which is a polyatomic ion)  = CO3^2-

Since the sum of the oxidation numbers must be zero, we need two sodium atoms for one carbonate.

Na2CO3

Fe2O3 is iron (III) oxide

The iron has an oxidation number of +3 and we name metal-nonmetal compounds using the Stock system.  The Stock system is named in honor of Alfred Stock, its inventor.  In the Stock system, when a metal has more than one possible oxidation number, we include a Roman numeral to indicate its oxidation number.