Write the formula for the following transition metal ionic compounds:

Question

Copper (I) oxide: Why is it Cu2O? How do I get that?

Nickle (II) sulfide: Why is it NiS? How do I get that?

Silver (I) chloride: Why is it AgCl? How do I get that?

Answer 1

In compounds other than peroxides, oxygen (O) is 2- and since they tell you copper is 1+ , you need 2 of them. You know Cu is 1+ because of the Roman numeral in parentheses. So, Cu2O is the correct formula for copper(I) oxide.

Again, the number in parenthesis tells you the charge on the Ni. Here it is 2+. S is 2- so it takes 1 Ni to balance the 1 S and so you have NiS.

Silver(I) chloride tells you that Ag has a 1+ and since Cl is 1-, you have AgCl

If you don't know how to tell the charge when the Roman number isn't given to you, like for Cl or S or O, etc., you look at the periodic table and for groups 1,2, and 3, (I - III) the charge is 1+, 2+ and 3+. Then for groups 5, 6, and 7 (XV - XVII), the charge is 3-, 2-, and 1-.