Drawing the Lewis Structure for HCO3-
Transcript: This is the HCO3 minus Lewis structure. For HCO3-, we have a total of 24 valence electrons. When we see an H in front of a polyatomic structure like the CO3- here, that means the H will be attached on the outside of one of the Oxygens. So we'll put Carbon at the center, and then we'll put an OH over here. That takes care of the H and one of the Oxygens. Then for the other Oxygens, we can just put them like this here.
So we have 24 valence electrons. We'll put two between the atoms to form chemical bonds--we've used 8--and then on the atoms on the outside, 10, 12, and 20. Then we'll put the remaining 4 here to fill the octet on the Oxygen: 24. We've used all 24 valence electrons. Hydrogen has 2 valence electrons; its octet is full. And then the Oxygens each have 8 valence electrons, so their octets are satisfied, as well.
However, Carbon only has 6 valence electrons. We need two more valence electrons to fill the octet and we don't have any more because we've used all 24. The solution is to take two of these valence electrons from the Oxygen and share them between the Oxygen and Carbon. This Oxygen still has 8 valence electrons, but this Carbon here in the center also has 8 valence electrons, so its octet is full by sharing those valence electrons to form a double bond. We're still using 24 valence electrons, but now each atom has an octet in the HCO3 Lewis structure.
So that's the Lewis structure for HCO3-. This is Dr. B., and thanks for watching.