The Lewis structure for CO₃, which is the carbonate ion, is illustrated as follows:
O
|
C = O
|
O
In the carbonate ion (CO₃²⁻), the central carbon atom is double-bonded to one oxygen atom and single-bonded to two other oxygen atoms. Each of the single-bonded oxygen atoms carries a negative charge, while the double-bonded oxygen does not carry any formal charge. The overall charge of the ion is -2, reflecting the negative charges on the singly bonded oxygen atoms.
This arrangement allows carbon to have a total of four bonds, fulfilling the octet rule, as it has a total of eight electrons surrounding it. The formal charges on the atoms can be calculated to ensure that the structure is stable:
- Carbon: 4 valence electrons – (0 non-bonding electrons + 1/2 x 4 bonding electrons) = 0
- Double-bonded Oxygen: 6 valence electrons – (4 non-bonding electrons + 1/2 x 2 bonding electrons) = 0
- Each Single-bonded Oxygen: 6 valence electrons – (6 non-bonding electrons + 1/2 x 2 bonding electrons) = -1
Thus, the Lewis structure clearly shows the bonding and gives insight into the geometry and reactivity of the carbonate ion.