Lewis Structure of CHO2- (or HCO2-) (With 6 Simple Steps)

Lewis Structure of CHO2- (HCO2-)

I’m super excited to teach you the lewis structure of HCO2- ion in just 6 simple steps.

Infact, I’ve also given the step-by-step images for drawing the lewis dot structure of HCO2- ion.

So, if you are ready to go with these 6 simple steps, then let’s dive right into it!

Lewis structure of HCO2- (or CHO2-) contains one double bond between the Carbon atom (C) & one Oxygen atom (O) and the rest other atoms are single bonded with each other. The Carbon atom is at the center and it is surrounded by 2 Oxygen atoms and one Hydrogen atom. The single bonded Oxygen atom has -1 formal charge.

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of CHO2- ion).

6 Steps to Draw the Lewis Structure of HCO2- ion

Step #1: Calculate the total number of valence electrons

Here, the given ion is HCO2- (methanoate ion). In order to draw the lewis structure of HCO2- ion, first of all you have to find the total number of valence electrons present in the HCO2- ion.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in HCO2- ion

  • For Hydrogen: 

Hydrogen is a group 1 element on the periodic table.

Hence, the valence electron present in hydrogen is 1 (see below image).

  • For Carbon:

Carbon is a group 14 element on the periodic table.

Hence, the valence electrons present in carbon is 4 (see below image).

  • For Oxygen:

Oxygen is a group 16 element on the periodic table.

Hence, the valence electron present in oxygen is 6 (see below image).

Hence in a HCO2- ion, 

Valence electrons given by Hydrogen (H) atom = 1
Valence electrons given by Carbon (C) atom = 4
Valence electrons given by each Oxygen (O) atom = 6
Electron due to -1 charge, 1 more electron is added
So, total number of Valence electrons in HCO2- ion = 1 + 4 + 6(2) + 1 = 18

Step #2: Select the center atom

While selecting the atom, always put the least electronegative atom at the center. 

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table).

Here in the HCO2 molecule, if we compare the carbon atom (C), oxygen atom (O) and hydrogen atom (H), then hydrogen is less electronegative than carbon and oxygen. But as per the rule, we have to keep hydrogen outside.

So, carbon (which is less electronegative than oxygen) should be placed in the center and the remaining oxygen atoms as well as hydrogen atom will surround it.

step 1

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of HCO2 molecule, put the two electrons (i.e electron pair) between the carbon-oxygen atoms and carbon-hydrogen atoms to represent a chemical bond between them.

step 2

These pairs of electrons present between the Carbon-Oxygen atoms as well as between the Carbon & Hydrogen atoms form a chemical bond, which bonds these atoms with each other in a HCO2 molecule.

Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom

Don’t worry, I’ll explain!

In the Lewis structure of HCO2, the outer atoms are hydrogen atom as well as oxygen atom.

Hydrogen already has a duplet (see below image).

So now, you have to complete the octet on oxygen atom (because oxygen requires 8 electrons to have a complete outer shell).

step 3

Now, you can see in the above image that the oxygen atom forms an octet.

Also, all the 18 valence electrons of HCO2- ion (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch.

Let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond

In this step, we have to check whether the central atom (i.e carbon) has an octet or not. 

In simple words, we have to check whether the central Carbon (C) atom has 8 electrons or not.

step 4

As you can see from the above image, the central atom (i.e carbon) has only 6 electrons. So it does not fulfill the octet rule.

Now, in order to fulfill the octet of a carbon atom, we have to move the electron pair from the outer atom (i.e oxygen atom) to form a double bond.

step 5

Now you can see from the above image that the central atom (i.e carbon), is having 8 electrons. So it fulfills the octet rule.

Step #6: Final step – Check the stability of lewis structure by calculating the formal charge on each atom

Now, you have come to the final step and here you have to check the formal charge on oxygen atom (O), carbon atom (C) as well as hydrogen atom (H).

For that, you need to remember the formula of formal charge;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

step 6
  • For Hydrogen:
    Valence electron = 1 (as it is in group 1)
    Nonbonding electrons = 0
    Bonding electrons = 2
  • For Carbon:
    Valence electrons = 6 (as it is in group 16)
    Nonbonding electrons = 0
    Bonding electrons = 8
  • For double bonded Oxygen:
    Valence electrons = 6 (as it is in group 16)
    Nonbonding electrons = 4
    Bonding electrons = 4
  • For single bonded Oxygen:
    Valence electron = 6 (as it is in group 16)
    Nonbonding electrons = 6
    Bonding electrons = 2
Formal charge=Valence electronsNonbonding electrons(Bonding electrons)/2
H=102/2=0
C=408/2=0
Double bonded O=644/2=0
Single bonded O=662/2=-1

Let’s keep these charges on the atoms in the above lewis structure of HCO2 molecule.

step 7

As you can see in the above sketch, there is one -ve charge on the single bonded oxygen atom, which indicates the -1 formal charge on the HCO2 molecule.

Hence, the above lewis structure of HCO2- ion is the stable lewis structure.

Each electron pair (:) in the lewis dot structure of HCO2- ion represents the single bond ( | ). So the above lewis dot structure of HCO2- ion (methanoate ion) can also be represented as shown below.

CHO2- Lewis structure

Related lewis structures for your practice:
Lewis Structure of PF6-
Lewis Structure of CNO-
Lewis Structure of BrO2-
Lewis Structure of N2O4
Lewis Structure of COF2 

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