What is the chemical name for limestone, #"CaCO"_3# ?
The trick here is to realize that you're dealing with an ionic compound, which implies that the compound contains a cation and an anion.
As you know, ionic compounds are formed when a metal reacts with a non-metal, so start by identifying your metal.
In this case, calcium,
#"Ca"^(2+) ->#the calcium cation
Now, the anion is actually a polyatomic ion made up of one carbon atom and three oxygen atoms. This polyatomic anion is called the carbonate anion and carries a
#"CO"_3^(2-) ->#the carbonate anion
When naming an ionic compound, we always start with the cation metal and end with the anion. In your case, you will have
#"CaCO"_3 ->#calcium carbonate