HCN Lewis Structure, Molecular Geometry, Hybridization, and Polarity



Prussic acid is another name for hydrogen cyanide or HCN.

It’s a liquid that has no color, is exceedingly combustible, and is poisonous. HCN can be found as a liquid or a gas.

The components of this weak acid are carbon, hydrogen, and nitrogen. It has a linear geometry with a triple bond between carbon (C) and nitrogen (N).

This blog article will help you understand the HCN lewis structure, hybridization, molecular geometry, and molecular orbital diagram.

Lewis structure of HCN

Before going towards the HCN Lewis structure, let us understand some general terms used in it.

Valence Electron

Valence electrons are the total number of electrons present in the atom’s outermost shell. Only valence shell electrons involve in bond formation. These valence electrons either share or are transferred (completely or partially) for bond formation.


Valance electrons are electrons in the outermost shell that are vital for bonding and forming molecules.

Octet Rule

The Octet Rule states that every atom likes to have eight valence electrons because this is the most stable and low-energy state.

HCN Lewis Structure

HCN Lewis Structure contains a single bond between hydrogen and a carbon atom. In addition, a triple bond is formed between the carbon and nitrogen atoms with a lone pair on nitrogen. The hydrogen and nitrogen atoms surround the carbon atom, which is located in the middle.

Steps to Remember While Drawing the Lewis Structure

To draw the Lewis structure of a molecule, there are a few general steps to follow. The number of steps can be adjusted depending on the molecule or ion’s complexity. We’ll look at each stage of drawing the HCN Lewis Structure. 

  • Calculate the total number of electrons in the valence shells.
  • Choosing the center atom
  • Place the valence electron
  • Draw lone pairs.

Draw the HCN Lewis Structure in 3 Easy Steps

The Lewis structure merely takes into account the electrons present in the valence shell, neglecting the inner shell’s electrons. A dot represents a lone pair of electrons in a Lewis structure, whereas a straight line indicates a bond pair of electrons.

Step # 1

To Determine the Total Number of Valence Electrons

While drawing the HCN lewis structure we should know that hydrogen cyanide is made of three elements: hydrogen, carbon, and nitrogen. Hydrogen lies in the IA group of the periodic table with one valence electron. Carbon belongs to group IVA element with four electrons in its outermost shell, while Nitrogen is in-group VA of the modern periodic table with five electrons in its outermost shell.

NOTE: To calculate the total outermost electrons of a particular element in molecule, multiply the number of atoms of particular element by its valence shell electrons.

Now let us calculate the Valence Shell Electron of hydrogen cyanide.

  • For Hydrogen

Hydrogen belongs to the IA group of the modern periodic table.

Hence, it has only one electron in its valence shell.

Mathematical Representation

Valence electron (1)* no. of atom (1) = 1

Valance electrons of hydrogen  HCN (Hydrogen Cyanide)

  • For Carbon

As carbon is an IVA element of the periodic table,

Therefore, the valence electrons in the outermost shell of carbon are four.

Mathematical representation

Valence electron (4)* no. of atom (1) = 4

    Valance electrons of Carbon  HCN (Hydrogen Cyanide)

  • For Nitrogen

As nitrogen is a VA element in the modern periodic table,

Therefore, nitrogen has five valence electrons.

Mathematical representation

Valence electron (5) * no. of atoms (1) =5

   Valance electrons of Nitrogen  HCN (Hydrogen Cyanide)     

To calculate the total valence electrons, add the valence electrons from all three atoms; the total number of valence electrons present is 1+4+5=10.

Hence, the valence electrons in HCN = 10.

Step # 2

Determine the Central Metal Atom:

According to the rule, the atom with the lowest electronegativity value would occupy a central place. The electronegativity of hydrogen, carbon, and nitrogen is 2.2, 2.55, and 3.04, respectively.

Here, hydrogen cannot serve as the central atom. It’s because the hydrogen atom has only one electron, it cannot form a bond with two atoms (carbon and nitrogen).

You can select the center atom from either carbon or nitrogen. As carbon is least electronegative than nitrogen, so, the carbon atom wins the central place here.

Lewis structure of HCN (Hydrogen Cyanide)Step # 3

Place the Valence Electrons around the Atoms

Hydrogen has one, carbon contains four, and nitrogen has five electrons around its atom.

lewis structure of HCNNow, hydrogen becomes stable if it shares its electron with the carbon atom. Hydrogen wants to be stable. That’s why it happily shares its only electron and makes a single bond with the carbon atom.

After satisfying the hydrogen atom, let’s move toward the carbon atom and make it happy. Carbon is left with three electrons as they donate one to the hydrogen atom. Now carbon also wants to be stable, share the remaining three electrons with nitrogen, and make a triple bond.

               Lewis structure of HCN

Carbon completes its octet by making a triple bond with nitrogen and a single bond with hydrogen. Similarly, nitrogen possesses a complete octet since it only requires three electrons to complete the octet that it gains by sharing electrons with carbon. The other two electrons on the nitrogen atom are non-binding.

Lewis structure of HCNWhy Do You Need to Know About HCN Lewis Structure?

Lewis structures are important in predicting the geometry, polarity, and reactivity of compounds (organic and inorganic). Knowing an atom’s Lewis structure helps you predict how it will bond and how many bonds it will make.

This information will ultimately help you to understand the structure of molecules as well as their chemical characteristics.

Knowing about the HCN Lewis structure is important for several reasons.

  • First, it helps us understand the chemical bonding and geometry of the molecule, which in turn can give us insights into its properties and behavior. For example, knowing that HCN is a polar molecule can help us predict its solubility in different solvents and its interactions with other polar or charged molecules.
  • Second, understanding the HCN Lewis structure is essential for studying chemical reactions involving this molecule. By knowing the positions and charges of the atoms and electrons, we can predict which bonds are likely to break or form during a reaction, and what products may result.
  • Third, HCN is an important molecule in several industrial and biological processes, such as the production of synthetic fibers and the detoxification of cyanide in the body. Knowledge of the HCN Lewis structure can help us understand how these processes work and how they can be optimized or controlled.
  • Finally, understanding the HCN Lewis structure is crucial for safety considerations. HCN is a highly toxic and reactive molecule, and proper handling and disposal procedures are necessary to prevent accidents and protect human health and the environment. Knowing how HCN interacts with other molecules and how it can be transformed or degraded can help us design safer and more effective strategies for handling and disposing of this hazardous substance.

The Molecular Geometry of Hydrogen Cyanide

The molecular geometry of any particular molecule contributes to the study of its three-dimensional structure, atom arrangement, and form.

HCN is an AX2 molecule, where A is the central atom and X is a bonded atom with the core atom. Furthermore, according to VSEPR theory, any molecule with an AX2 structure would have linear geometry. 

Hence, hydrogen cyanide possesses linear molecular geometry.

Molecular geometry of hcn

Hybridization of HCN

HCN comprises two sigmas and two pi bonds. One sigma bond connects carbon to hydrogen (C-H), whereas the other connects carbon to nitrogen (C-N). Two pi bonds are formed between carbon and nitrogen. However, hydrogen cyanide is an sp hybridized molecule.

Hybridization of the C atom 

In hydrogen cyanide, the carbon atom is connected to nitrogen by a triple covalent bond that consists of two pi and one sigma bonds. sp hybridized orbitals overlap to form a sigma bond, while two pi bonds are formed by the overlapping of un-hybridized p orbitals.

 Hybridization of the N atom 

 Nitrogen possesses two degenerate p and two sp hybrid orbitals. One sp orbital forms a sigma bond with the carbon atom’s sp hybrid orbital, while the other contains a lone pair of electrons.

HCN hybirdization


HCN Bond Angle & Shape

The bond angle is the angle formed by the central atom and the bounded atoms.  The number of bonded atoms determines the bond angle. A larger bond angle would be the result of less repulsion.

Once you know the molecular geometry and Lewis structure of any molecule. It’s become easy to estimate its polarity and bond angle. The HCN molecule possesses linear geometry with a bond angle of 180 degrees.


HCN bond angle


Is HCN polar or non-polar?

HCN is a polar molecule. The polarity of any molecule depends upon its electronegativity value, geometry, and dipole moment.

The greater value of electronegativity makes the covalent bond polar. An electronegativity value for hydrogen is 2.2, carbon possesses 2.55, and nitrogen has 3.04.

A polar molecule has uneven electronegativity among its constituent atoms. This causes an electric charge imbalance across the molecule, giving it a net dipole moment.

  HCN is polar or non polar                              


Any molecule that differs in its electronegativity at each dipole moment is regarded as polar.

Hence, hydrogen cyanide is a polar molecule.

 Now let’s summarize what you’ve learned up till now. 



Hydrogen Cyanide



Valence shell electrons




Molecular weight


Molecular geometry


Dipole moment


Bond angle




The Molecular Orbital Diagram of HCN

 Molecular orbital theory tells you about the location of an electron within a molecule. Generally, two types of molecular orbitals are formed by combining atomic orbitals.

  1. Bonding molecular orbital (σ, π)
  2. Non-bonding molecular orbital ( σ*, π* )

In bonding molecular orbitals, electrons spend their time between the nuclei, while electrons are located away from nuclei in the anti-bonding molecular orbital. Bonding orbitals are low in energy as compared to anti-bonding orbitals.

Electrons first fill lower energy orbitals (bonding) and then go towards the higher energy orbital (anti-bonding).

Are you done with the basics of molecular orbital theory?

Now move toward the molecular orbital (MO) diagram of hydrogen cyanide. You can draw an MO diagram of HCN simply by following the following steps.

Steps to Draw an MO Diagram

  • Calculate the valence electron of carbon, hydrogen, and nitrogen, which are all 10.
  • Determine whether the molecule has a heteroatomic orbital or a homoatomic orbital. Surely, hydrogen cyanide has a hetero-atomic molecular orbital (as it contains different atoms).
  • Fill molecular orbitals by taking into account their energy (i.e., bonding molecular orbitals are kept lower than anti-bonding orbitals).
  • Now, draw the MO diagram for hydrogen cyanide and fill the molecular orbital with electrons.

           Molecular orbital diagram of HCN


The molecular orbital diagram helps you to determine the various properties of hydrogen cyanide, which include its bond order, magnetism (para-magnetic or diamagnetic), and bond length.

HCN Physical and Chemical Characteristics

  • HCN occurs in the form of white powder.
  • It smells like sour almonds in an aqueous state.
  • Its molecular weight is 27.0253 g/mol.
  • The density is 687 kg/m3.
  • The melting point of hydrogen cyanide is -13.4 °C.
  • Its boiling point is 25.6 °C.

Uses of HCN

  • HCN is an important industrial chemical, with over a million tons of production per year worldwide.
  • Hydrogen cyanide serves as a fumigant to prevent pests.
  • It’s used in the manufacturing of plastics, paints, synthetic fibres, and many other chemicals.
  • HCN also has uses in metal cleaning and ore extraction.
  • used in electroplating, printing, dying, and photography.

Dangerous Effects of HCN

  • Early symptoms of hydrogen cyanide poisoning include headaches, nausea, dizziness, confusion, and sleepiness.
  • Prolonged exposure can cause unconsciousness, coma, and even death.
  • Due to its severe toxicity, hydrogen cyanide hinders the body from correctly utilizing oxygen.
  • Survival after high exposure may result in long-term complications for the brain and nervous system.

Industry Uses of HCN 

HCN has several industrial applications. Here are some of the most common uses of HCN:

  1. Production of synthetic fibers: HCN is used in the production of synthetic fibers such as nylon, acrylic, and modacrylic. These fibers are used in a variety of products, including clothing, carpets, and upholstery.

  2. Mining: HCN is used in the mining industry for the extraction of gold and other precious metals from ores. It forms complexes with metals such as gold, silver, and copper, which can be separated and purified.

  3. Chemical synthesis: HCN is a versatile reagent that can be used in a variety of chemical reactions, such as the synthesis of pharmaceuticals, agrochemicals, and plastics.

  4. Fumigation: HCN is a potent fumigant that can be used to control pests and insects in stored products, such as grains, fruits, and vegetables.

  5. Electroplating: HCN is used in the electroplating industry as a stabilizer for certain electroplating solutions.

  6. Detoxification: HCN is used in the detoxification of cyanide in wastewater treatment plants and in the processing of certain foods, such as cassava, which contain natural cyanide.

  7. Chemical warfare: HCN has been used as a chemical weapon in the past, but its production and use are now banned under international law.

It’s worth noting that HCN is a highly toxic and flammable substance, and proper safety measures must be taken when handling and using it.


HCN Lewis structure contains one lone pair on the nitrogen atom, a triple covalent bond between carbon and the nitrogen atom, and a single bond between carbon and hydrogen. It possesses linear geometry with a 180o bond angle.

The hybridization of the molecule has been discussed, which is the sp type. It’s a nonpolar molecule and different factors can affect the polarity of the molecule, which include electronegativity, dipole moment, and the molecular geometry of the molecule.

Hydrogen cyanide has different physical and chemical characteristics, which have been discussed in that article. It is used in the production of many chemicals, paints, and synthetic fibres.

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Frequently Asked Questions: FAQs


What is the molecular shape and bond angle of HCN?

HCN Lewis Structure has linear geometry with a bond angle of 180 degrees. According to VSEPR, a molecule that comes under the AX2 category possesses a linear shape. However, in HCN, ‘A’ is the central atom and ‘x’ are bonded atoms with it. Therefore, it possesses linear molecular geometry.

Is hydrogen cyanide still used?

HCN is a chemical that is used to make acrylonitrile, cyanide salts, and colors. It is also serving as a fumigant in horticulture. Commercial applications include electroplating, chemical synthesis, mining, and the creation of synthetic textiles, polymers, dyes, and insecticides.

How many lone pairs are in an HCN Lewis Structure?

HCN Lewis Structure contains a single covalent bond between carbon and hydrogen and a triple bond between nitrogen and a carbon atom. It has ten electrons, out of which 8 participate in bonding while two are present as lone pairs on the terminal nitrogen atom. Therefore, HCN Lewis Structure possesses one lone pair on the nitrogen atom.

What is the formal charge of each atom in the HCN Lewis Structure?

The carbon atom has a formal charge of zero, the nitrogen atom has a formal charge of +1, and the hydrogen atom has a formal charge of -1

What is the Lewis acid-base behavior of HCN?

HCN can act as a Lewis acid, accepting an electron pair from a Lewis base, or as a weak Lewis base, donating an electron pair to a Lewis acid.

What are some applications of HCN in the industry?

HCN is used in the production of nylon, acrylic fibers, and plastics, as well as in the mining industry for extracting gold and other precious metals.


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