## Jaimesha 4 years ago How do I know when to use Roman Numerals when writing a chemical formula? Anyone know? @Mathematics

1. wcaprar

You're going to use a Roman numeral if the element is a transition metal.

2. Jaimesha

Thankyou, but how do you know what number to wite?

3. wcaprar

It's going to be based on the charge. For example: Cu3+ (III) Cu2+ (II) Cu1+ (I)

4. Jaimesha

How does Cu have a 3+ charge? My teacher didnt do the charges for the transition metals so I'm a little lost

5. Jaimesha

For instance Lead(IV) oxide. How do you get the IV?

6. wcaprar

Oxygen has a charge of 2-. So that would mean that with PbO the lead has a charge of 2+ and the oxygen has a charge of 2-, giving it an overall charge of 0. But in your case there is a charge of 4- on the lead (because it is Lead (4) oxide), so if oxygen still has a charge of 2-, then there must be two oxygens to make the compound neutral. Therefore, PbO2

7. wcaprar

Does that make sense?

8. Jaimesha

Thankyou:) that makes much sense

9. Jaimesha

I mean I kind of get it better now. But I'm still somewhat confused' but you made it better:)

10. wcaprar

If you have anymore questions, ask, and hopefully I can better clarify it