# What is the chemical name for limestone, "CaCO"_3 ?

Mar 1, 2017

Calcium carbonate.

#### Explanation:

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, $\text{Ca}$ is the metal. Calcium is located in group 2 of the Periodic Table, which means that it forms $2 +$ cations. This means that you're dealing with the calcium cation, which looks like this

${\text{Ca}}^{2 +} \to$ 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 $2 -$ charge.

${\text{CO}}_{3}^{2 -} \to$ 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

${\text{CaCO}}_{3} \to$ calcium carbonate