HCN Lewis Structure, Molecular Geometry, Shape, and Polarity

HCN (Hydrogen Cyanide) is a colorless or pale blue liquid below 78-degree Fahrenheit. If not in the liquid form, it can be in the gas form. It is colorless gas above 78 degrees Fahrenheit. HCL interferes with the regular use of Oxygen by the organs of the body. The exposure can be rapidly fatal. It has a distinctive bitter almond odor, and some also say that it smells like some old sneakers smell. HCL can also be used as a solution in water. There are few other names like Formonitrile, Hydrocyanic acid, and Prussic acid.HCN lewis structure, molecular geometry, shape, and Polarity

It is an essential systemic agent. One can release it as a liquid spray or a gas into the indoor air or outdoor air or can be used to contaminate food or water. It can affect the body by ingestion, inhalation, skin contact, or eye contact. Understanding of HCL can be beneficial to you if you are a chemistry freak. In this article, you can get a detailed understanding of HCN Lewis structure and Molecular geometry.

You must be aware that to understand the molecular geometry of HCL; one must know HCL Lewis structure. According to VSEPR theory, the atoms are going to spread out as far as possible while still staying connected to that central carbon. So assuming that the valence shell electron pairs are repelling each other, there will be a Hydrogen on one side and the Nitrogen on the other hand of the central atom Carbon.

How to Draw HCN Lewis Structure?

  • To draw Lewis structure is extremely easy and quick. First of all, refer to the periodic table and count the electrons by matching the columns. You can find out that Hydrogen brings 1, Carbon brings 4, and Nitrogen carries five each, which means there are 10 electrons in total.
  • Write them down on the paper with probably the least electronegative atom in the center and draw the bonds, then put some electrons in the bond. There should be at least one bond each that makes four electrons.
  • The next step is to fill the outer shells until there is no space in the outer atoms or there are no electrons left. There are already four electrons, which means the Hydrogen is already filled as it can only hold two particles.

Lewis structure

  • As there are already four electrons, cover Nitrogen with other six atoms. As HCN has ten valence electrons for the Lewis structure, now there are no electrons left. The Nitrogen is having a full octet by having eight electrons in total.
  • After that, move electrons from your outer atoms to your central atoms until they also have a full octet. Carbon needs eight electrons, and it currently has four. So, transfer two electrons from the Nitrogen and make it double bond.
  • Now, Carbon has six electrons, but there are still two left. So, once again get rid of two more electrons of N and make it a triple bond. Notice that the Carbon now has eight electrons and so the Nitrogen. Hydrogen already has its max that is two.

This is how Lewis dot structure of Hydrogen Cyanide goes! Once the least electronegative atom in the center fills the outer atoms, move outer electron pairs to the center until they have a full octet. It should be called like – H single bond C triple bond N with a lone pair of electrons sitting on the end.

Note: Hydrogen is an exception. It is never at the center.

HCN Molecular Geometry

Molecular geometry is known as the specific three-dimensional arrangements of atoms in molecules. Lewis structure is used to predict the overall geometry of a molecule or ion and the number of electrons surrounding a central atom. Electrons around the Carbon atom are involved in chemical bonds.


HCN molecular geometry is linear. A, X, and Notation theory can also be used to make sure about the right molecular geometry. Here, A would be the central carbon, X would be the number of atoms attached to that central carbon (In HCN, there are two – Hydrogen and Nitrogen) and N would be the number of lone pair electrons or nonbonding electron pairs.

If you want to confirm the status, then look at up at the table. The very first one is AX2. It is a very simple molecule, and you can see that it is linear with the bond angles of 180 degrees. You can also memorize that AX2 is a linear molecular geometry. So, that’s the molecular geometry for HCN.

HCN 3d imageHCN Bond Polarity

When there is different electronegativity in the atoms, there are cases of polarities. When there are complicated molecules, it becomes necessary to consider the expectations of molecular polarities that born from the combination of all the single bond polarities. If there are two atoms and both of them are not identical, the magnitude of the vector will not be zero, and the bond will not be polar.

Talking about HCN, first of all, refer to this article once again and find out that HCN. Hydrogen Cyanide is linear. Carbon is more electronegative than Hydrogen. So, there is a vector pointing from Hydrogen to the Carbon. Moreover, Nitrogen is more electronegative than Carbon and even the Hydrogen, so there might be a bond vector indicating from Carbon to Nitrogen.

HCN is Polar

The Hydrogen to Carbon and Carbon to Nitrogen vectors add to indicate that the Hydrogen is going towards Nitrogen. HCN is polar with the little bit positive H and a little bit negative N. If you want to make this process fast then understand the concept of vectors. Think of the polar bond as a vector; pointed from the positively charged atom to the negatively charged molecule.

Sum Up…

So, that’s all for the HCN lewis structure, molecular geometry, shape, and polarity. I hope you have found this article useful and it will help you to understand HCN as a whole. Whenever you think that you are having some confusions regarding any questions regarding the geometry of Hydrogen Cyanide molecules, this simple explanation will be just one click away. Always have faith in your learning and keep showering your love to this subject to be the best in this magical world of Chemistry.

Quick Summaries – Revision and Notes

  • HCN lewis structure is – H single bond C triple bond N
  • HCN has ten valence electrons.
  • The shape of HCN is linear.
  • HCN bond angles of 180 degrees.
  • Hydrogen Cyanide is Polar.
  • Hydrogen can never be at the center.
  • HCN is covered under AX2, which is a linear molecular geometry.
  • Always consider the concept of vectors before going further to find whether the bond is polar or nonpolar.
  • The size of a vector is proportional to the difference in electronegativity of the two atoms.
  • If electron pair repulsion is concerned, one can also consider the double bonds and triple bonds as a single bond.
  • When there are simple molecules, try to consider a first approximation using simple figures as it is more likely to be true.

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