Chemical Bonding: HCO₂^- Lewis Structure

Drawing the Lewis Structure for HCO₂^-

Viewing Notes:

• There are a total of 18 valence electrons in the HCO₂^- Lewis structure.
• HCO₂^- is also called Formate Ion.
• Carbon (C) is the least electronegative atom and goes at the center of the HCO₂^- Lewis structure.
• With HCO₂^- you'll need to form a double bond between one of the Oxygen atoms and the Carbon atom to fill the octets and still use only the 18 valence electrons available for the molecule.
• Remember to put brackets around the HCO₂^- Lewis dot structure with a negative one sign outside the brackets to show the structure is an ion.

Transcript: For the HCO2- Lewis structure, we have a total of 18 valence electrons. Hydrogens always go on the outside of Lewis structures. Carbon is less electronegative than Oxygen, so we'll put a Carbon in the center, and then we'll put the Oxygens on the Carbon. We have a total of 18 valence electrons for the HCO2- Lewis structure. We'll put two between atoms to form chemical bonds, and we'll go around the outside. So we've used 2, 4, 6, 8, and 18.

So at this point, we've used all 18 valence electrons. The Oxygens have eight valence electrons, so their octets are full, and the Hydrogen has two valence electrons, so it has a full outer shell, as well. However, the Carbon only has six, so we're going to have to share some electrons to get Carbon to have an octet. Let's take these two valence electrons and move them to the center to form a double bond. So we're still using 18 valence electrons. The Oxygen, it still has eight valence electrons; but now the Carbon, it has eight valence electrons. So we've used all 18 valence electrons, and each of the atoms has its outer shell full.

If we check the formal charges, we'll see that all the atoms have a formal charge of zero except this Oxygen right here. It has a formal charge of negative one. That makes sense, though, because we have a negative one up here so it needs to match our Lewis structure for HCO2-. One last thing: since we do have an ion, we should put brackets around the structure and put a negative sign on the outside to show that it is an ion.

So that's the Lewis structure for HCO2-. This is Dr. B., and thanks for watching.