Question

Why do we need to use number prefixes with molecules rather than ionic compounds?

Answer 1

In an ionic compound the metal has a charge. For example Magnesium Chloride isn't Magnesium Dichloride becuase there is only one available option. Mg is a 2+ and chlorine is a 1-. There fore Magnesium chloride will always be MgCl2. No need to specifiy there are two chlroines. For metals like Iron where it has more than one oxidation number we use roman numerals to specify which one it is. Like Fe(ii)SO4. This means The iron is a 2+ here. or we could say Fe2O3. That would be called iron three oxide becuase the iron has a charge of +3, the O -2. Does that help? Or should I explain further?

Answer 2

Thanks you very much... so if I have this straight it is because the information isn't needed to define the compound because you can tell from the positive and negative ionic charge the ratio between them. Is that right? Thanks again!

Answer 3

Woot woot! perfect.