Lewis structure

Here is the lewis dot structure of carbonate (CO3 2-):

step 1: Find the total number of valence electrons. Check the periodic table, the atomic number of C is 6 and of O is 8, so in C there is 4 valence electrons and in O there is 6. The total number of valence electrons of carbonate is -2.

step 2: Confirm the central atom. Because C is the least electronegative atom so choose it as the central atom and the three oxygen atoms surround it.

step 3: Fulfill the octet for all the atoms. Put two electrons between two atoms to show the chemical bonding between them. If the central atom does not possess octet configuration then move a pair of electrons from outside atom and arrange it in between the central atom and the outside atom so that double bonds are formed.

Resonance structures

There are three resonance structures for CO3 2-. The carbon-oxygen double bond can be positioned with any of the three oxygen atoms, the three structures are equivalent.