To draw the Lewis structure for the carbonate ion (CO32-), we need to follow several steps to ensure that we represent all the atoms and their valence electrons accurately.
- Count the total number of valence electrons: Carbon (C) has 4 valence electrons, and each oxygen (O) has 6 valence electrons. The carbonate ion has one carbon atom and three oxygen atoms, along with an additional 2 electrons due to the 2- charge.
- Calculating the total:
- Carbon: 4 electrons
- Oxygen x 3: 6 x 3 = 18 electrons
- Charge: 2 electrons
Total = 4 + 18 + 2 = 24 valence electrons.
- Place the atoms: Carbon is the central atom, surrounded by the three oxygen atoms.
- Connect the atoms: Draw a single bond between carbon and each oxygen atom. This uses 6 of the total electrons (3 bonds x 2 electrons per bond), leaving us with 18 electrons.
- Distribute remaining electrons: Begin placing the remaining lone pairs on the oxygen atoms. Each oxygen atom will receive 6 electrons in the form of three lone pairs.
- Check formal charges: Each oxygen bonded to carbon will initially have a formal charge of -1, resulting from having 6 – 1 (bonding to C) = 5 valence electrons. Therefore, we have to create a double bond between the carbon and one of the oxygen atoms, reducing the negative charge on that oxygen to zero and giving carbon a formal charge of zero.
After adjusting, we get the following Lewis structure:
In this structure, carbon is at the center, singly bonded to two oxygen atoms and doubly bonded to one oxygen atom, with the appropriate lone pairs shown. This structure satisfies the octet rule for each of the atoms involved.