Draw the Lewis Structure for HCO2 and Determine the Formal Charge of Each Atom

To draw the Lewis structure for HCO₂ (formate ion), we start by calculating the total number of valence electrons. Hydrogen (H) has 1 valence electron, carbon (C) has 4, and each oxygen (O) has 6 valence electrons. Since we have one hydrogen, one carbon, and two oxygens, the total is:

• 1 (H) + 4 (C) + 2 × 6 (O) = 1 + 4 + 12 = 17 valence electrons.

This gives us a total of 17 valence electrons to work with.

Next, we can start arranging the atoms. The central atom will be carbon (C), bonded to one hydrogen (H) and two oxygen (O) atoms. We can place one hydrogen atom attached to the carbon and then connect the carbon to the two oxygens. A common way to represent this is:

   H
    |
   C
  / \
 O   O

Now, we need to fulfill the octet rule for the oxygen atoms. We can place a double bond between the carbon and one of the oxygen atoms to achieve this, while the other oxygen will have a single bond with a negative charge, as shown below:

   H
    |
   C = O
  / 
 O-

Now, we need to assign formal charges to each atom in the structure. The formula for formal charge is:

Formal Charge = Valence Electrons – (Non-bonding Electrons + 0.5 × Bonding Electrons)

• Hydrogen (H):
  Valence Electrons = 1
  Non-bonding Electrons = 0
  Bonding Electrons = 2 (1 bond with C)
  Formal Charge = 1 – (0 + 0.5 × 2) = 0
• Carbon (C):
  Valence Electrons = 4
  Non-bonding Electrons = 0
  Bonding Electrons = 8 (1 bond with H and 2 bonds with O)
  Formal Charge = 4 – (0 + 0.5 × 8) = 0
• Oxygen (O with double bond):
  Valence Electrons = 6
  Non-bonding Electrons = 0
  Bonding Electrons = 4 (2 bonds with C)
  Formal Charge = 6 – (0 + 0.5 × 4) = 4 – 2 = +2
• Oxygen (O with single bond):
  Valence Electrons = 6
  Non-bonding Electrons = 6
  Bonding Electrons = 2 (1 bond with C)
  Formal Charge = 6 – (6 + 0.5 × 2) = 6 – (6 + 1) = 6 – 7 = -1

So, the formal charges on the atoms are:

• Hydrogen: 0
• Carbon: 0
• Oxygen (double bond): +1
• Oxygen (single bond): -1

Thus, the Lewis structure for HCO₂ is complete, and we have determined that the formal charges are balanced, resulting in a net charge of 0 for the overall ion.