What is the charge on a carbonate ion (CO3^2-)? How does the number of electrons in the carbonate ion compare to the number of protons?

The carbonate ion (
3
2
−
CO
3
2−
​
) has a charge of -2. This means it has gained two extra electrons compared to the number of protons in its nucleus.

In a neutral atom of carbon (elemental carbon), there are 6 protons, and in a neutral oxygen atom, there are 8 protons. The carbonate ion (
3
2
−
CO
3
2−
​
) consists of one carbon atom and three oxygen atoms. Therefore, the total number of protons in the carbonate ion is
6
+
3
×
8
=
30
6+3×8=30 protons.

Since the carbonate ion has a charge of -2, it means it has gained two extra electrons. Electrons are negatively charged, so by gaining two electrons, the ion balances out its charge with the 30 protons in its nucleus, resulting in an overall charge of -2.