HCONH2 Lewis structure

HCONH₂ (formamide) has three hydrogen atoms, one carbon atom, one oxygen atom, and one nitrogen atom.

In HCONH₂ Lewis structure, there is a single bond between the carbon and nitrogen atom. The carbon is attached with one oxygen atom and one hydrogen atom, and the nitrogen is attached with two other hydrogen atoms. There are two lone pairs on the oxygen atom, and one lone pair on the nitrogen atom.

Alternative method: Lewis structure of HCONH₂

Rough sketch

• First, determine the total number of valence electrons

In the periodic table, hydrogen lies in group 1, carbon lies in group 14, oxygen lies in group 16, and nitrogen lies in group 15.

Hence, hydrogen has one valence electron, carbon has four valence electrons, oxygen has six valence electrons, and nitrogen has five valence electrons.

Since HCONH₂ has three hydrogen atoms, one carbon atom, one oxygen atom, and one nitrogen atom, so…

Valence electrons of three hydrogen atoms = 1 × 3 = 3
Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of one oxygen atom = 6 × 1 = 6
Valence electrons of one nitrogen atom = 5 × 1 = 5

And the total valence electrons = 3 + 4 + 6 + 5 = 18

Learn how to find: Hydrogen valence electrons, Carbon valence electrons, Oxygen valence electrons, and Nitrogen valence electrons

• Second, find the total electron pairs

We have a total of 18 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 18 ÷ 2 = 9

• Third, determine the central atom

Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.

Now we have to choose the central atom from carbon, oxygen, and nitrogen. Place the least electronegative atom at the center.

Since carbon is less electronegative than oxygen and nitrogen, assume that the central atom is carbon.

Therefore, place carbon in the center and hydrogen, oxygen, and nitrogen on either side.

• And finally, draw the rough sketch

Lone pair

Here, we have a total of 9 electron pairs. And five bonds are already marked. So we have to only mark the remaining four electron pairs as lone pairs on the sketch.

Also remember that hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell. And all three (carbon, nitrogen, and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogens, oxygen, and nitrogen. But no need to mark on hydrogen, because each hydrogen has already two electrons.

So for oxygen, there are three lone pairs, and for nitrogen, there is one lone pair. And for carbon, there is zero lone pair because all four electron pairs are over.

Mark the lone pairs on the sketch as follows:

Formal charge

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

For carbon atom, formal charge = 4 – 0 – ½ (6) = +1

For oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

For nitrogen atom, formal charge = 5 – 2 – ½ (6) = 0

Here, both carbon and oxygen atoms have charges, so mark them on the sketch as follows:

The above structure is not a stable Lewis structure because both carbon and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

Convert a lone pair of the oxygen atom to make a new C — O bond with the carbon atom as follows:

Final structure

The final structure of HCONH₂ comprises a central carbon atom connected to an oxygen atom, a nitrogen atom, and a hydrogen atom. In this arrangement, the carbon atom forms a double bond with the oxygen atom and single bonds with the nitrogen and the hydrogen. Within this layout, the nitrogen atom is further single-bonded to two additional hydrogen atoms, fulfilling its octet by maintaining one lone pair. The oxygen atom also satisfies the octet rule by retaining two lone pairs alongside its double bond, while each carbon and hydrogen atom reaches its stable electronic state. This configuration represents the most stable state for the molecule because it results in a formal charge of zero for every atom. Accordingly, this specific electronic distribution serves as the definitive and most accurate Lewis representation of formamide.

Next: SeOBr₂ Lewis structure

External links

• https://oneclass.com/homework-help/chemistry/7047738-hconh2-lewis-structure.en.html
• https://www.chegg.com/homework-help/questions-and-answers/5-correct-lewis-structure-hconh2-cnh-h-6-8-4h-0-c-n-hh-o-h-b-0-h-c-n-h-h-d-h-ceo-nh-h-e-oa-q68923230
• https://www.coursehero.com/file/p1qsvub/Draw-the-best-Lewis-structure-for-HCONH-2-where-both-the-oxygen-and-nitrogen/