HOCN Lewis structure

HOCN (cyanic acid) has one hydrogen atom, one oxygen atom, one carbon atom, and one nitrogen atom.

In the HOCN Lewis structure, there is a single bond between carbon and oxygen atom, and a triple bond between carbon and nitrogen atom. The oxygen atom (with which the hydrogen atom is attached) has two lone pairs, and the nitrogen atom has one lone pair.

Alternative method: Lewis structure of HOCN

Rough sketch

• First, determine the total number of valence electrons

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

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

Since HOCN has one hydrogen atom, one oxygen atom, one carbon atom, and one nitrogen atom, so…

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

And the total valence electrons = 1 + 6 + 4 + 5 = 16

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

• Second, find the total electron pairs

We have a total of 16 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 = 16 ÷ 2 = 8

• 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 oxygen, carbon, 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 8 electron pairs. And three bonds are already marked. So we have to only mark the remaining five 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 (oxygen, carbon, and nitrogen) 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 hydrogen, oxygen, and nitrogen. But no need to mark on hydrogen, because hydrogen already has two electrons.

So for nitrogen, there are three lone pairs, for oxygen, there are two lone pairs, and for carbon, there is zero lone pair because all five 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 hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

For oxygen atom, formal charge = 6 – 4 – ½ (4) = 0

For carbon atom, formal charge = 4 – 0 – ½ (4) = +2

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

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

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

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

Since there are charges on both carbon and nitrogen atoms, again convert a lone pair of the nitrogen atom to make a new C — N bond with the carbon atom as follows:

Final structure

The final structure of HOCN has a central carbon atom linked to a nitrogen atom through a triple covalent bond and to an oxygen atom through a single covalent bond. In this arrangement, the carbon atom satisfies the octet rule by forming four total bonds, while the nitrogen atom fulfills its octet by forming the triple bond and retaining one lone pair. Within this layout, the oxygen atom reaches a stable octet by forming a single bond with the carbon, a single bond with a hydrogen atom, and maintaining two lone pairs. This configuration represents the most stable state for the molecule because it results in a formal charge of zero for every atom involved. Consequently, this specific electronic distribution serves as the definitive and most accurate Lewis representation of cyanic acid.

Next: SeS₂ Lewis structure

External video

• HOCN Lewis Structure: How to Draw the Lewis Structure for HOCN – YouTube • Wayne Breslyn

External links

• https://lambdageeks.com/hocn-lewis-structure/
• https://oneclass.com/homework-help/chemistry/7029396-hocn-lewis-structure.en.html