HCN Lewis Structure (in 5 steps): Amazing Guide


Hydrogen cyanide is a chemical compound that has the formula HCN. It is a gas (colorless) at room temperature that is extremely hazardous, but under some circumstances, it can also be a liquid. HCN smells strongly of bitter almonds and is frequently used as a warning sign at facilities where it is handled; however, not everyone can smell it because some people are anosmic (without the sense of smell). In the HCN Lewis structure molecule, the hydrogen atom (H) is covalently joined to the carbon atom (C), which is then joined to the nitrogen atom (N). The triple connection between the carbon and nitrogen atoms forms a linear molecule.

This substance has a distinguished history in chemistry and toxicology and is important in many industrial operations. It has historically been a chemical weapon, especially during World War I.

Natural sources of HCN include various plants, particularly in the seeds and leaves of a few fruit trees such as cherry laurels, bitter almonds, and apricots. Humans and numerous other species are very poisonous to HCN. It disrupts cellular respiration, stopping cells from utilizing oxygen, which can cause asphyxiation to happen quickly. Even relatively small quantities of exposure can be lethal.


The chemical molecule hydrogen cyanide is very reactive and has interesting chemical and physical characteristics. We’ll carefully examine its main chemical and physical features here:

Density: HCN gas has a lower density than air. It has a density of roughly 0.687 g/cm3 at standard pressure and temperature.

Solubility: Because HCN is extremely soluble in water, it can be transported easily in aqueous solutions.

Melting Point: The melting point of HCN is a very low -13.4 oC. Its volatility is a result of its low melting point.

Boiling Point: HCN has a boiling point of about 25.6 oC. HCN easily vaporizes into the air at ambient temperature due to its low boiling point.

Stability: When exposed to air and light, HCN is comparatively unstable. It can gradually break down into less harmful substances like hydrogen and cyanogen (C2N2), especially when exposed to ultraviolet (UV) light.

Vapor Pressure: Even at very low temperatures, HCN has a high vapor pressure. This indicates that, at temperatures below its boiling point, it quickly changes from a liquid to a gas.

Reducing Agent: In some chemical processes, HCN can function as a reducing agent. As an illustration, it can convert silver ions (Ag+) into silver cyanide (AgCN). In procedures like silver plating, this characteristic is utilized.

Weak Acidity: HCN is a weak acid. It is capable of dissociating in water to produce the ions cyanide (CN-) and hydronium (H3O+). Its mildly acidic behavior in aqueous solutions is caused by this dissociation.

              HCN + H2O ⇌ CN + H3O+

Combustion: Because HCN is combustible, it can take part in combustion processes. Nitrogen oxides (NOx), water, and carbon dioxide (CO2) can all be produced when they are ignited in the presence of oxygen.

2HCN + 3O2 → 2CO2 + 2H2O + N2 + 2NOx

Isomerization: Under some circumstances, HCN can isomerize to produce the substance isocyanic acid (HNCO). An isomer of HCN with unique chemical characteristics is called isocyanic acid.

Complex Formation: HCN can create stable metal cyanide complexes with a variety of metal ions. These complexes frequently have distinctive chemical characteristics and are vividly colored. For instance, the interaction between HCN and iron (III) ions results in the iconic blue pigment known as Prussian blue.

Applications of HCN:

Although hydrogen cyanide has several uses in a variety of industries, its utilization is mostly constrained by its severe toxicity.

Chemical Synthesis:

HCN is a key building block in the synthesis of numerous antibiotics, analgesics, and vitamins, among other medicinal substances. Some insecticides that are used to control pests in agriculture are derived from HCN or its compounds. It is employed in the creation of synthetic rubber and polymers.

Metallurgy and Mining:

Silver and gold are extracted from ores using HCN. Together, they create a stable complex that can be used to extract these metals from other minerals. HCN is used in metallurgy to purge antimony and arsenic impurities from base metals like copper and lead.


In agriculture, HCN can be used as a fumigant to get rid of pests in fruits, vegetables, and grains that are kept in storage. However, because of its toxicity, its use is strictly controlled.

Chemical Evaluation:

HCN is occasionally employed in chemical laboratories for a variety of analytical tasks, including figuring out how much nitrogen is present in organic molecules.

Manufacturing of Synthetic Fibers:

Synthetic fibers like nylon and acrylic are created using HCN.


Photographs were developed and fixed with HCN in earlier photographic processes.

Natural Product Extraction:

In the past, HCN has been used to extract natural compounds from plants, such as flavours and fragrances.

Military and Warfare:

During World War I, the Germans predominantly used HCN in chemical warfare. International treaties, however, forbid its use as a weapon. 

In Biology:

Because it disrupts cellular respiration, HCN is exceedingly harmful to most kinds of life, including humans. It prevents cells from utilizing oxygen for energy production by inhibiting the mitochondrial cytochrome c oxidase enzyme.

Insect Defense Mechanism:

HCN production is a defense mechanism used by some insects, including some species of millipedes. They release HCN when threatened, which deters or hurts predators.

Cyanogenic Plant Metabolism:

The ability to synthesize and store HCN in a bound, harmless form (like cyanogenic glycosides) is only possessed by a small subset of plants, referred to as cyanogenic plants. Enzymes are activated and release HCN when plant tissue is harmed, such as by herbivores or pathogens. By stopping the growth of herbivores, this release can safeguard the plant. Apple seeds and cherry pits are a couple of examples.

Plant Protection Mechanism:

Amygdalin is a substance found in some plants, especially those in the Rosaceae family (such as apple seeds and cherry pits), and it can produce HCN when plant tissue is harmed. This protects against herbivores in some way.

HCN Lewis structure:

For the HCN lewis structure, the octet rule is applied, which states that the atom needs to complete its valence shell electrons by sharing, gaining, and losing electrons. In lewis structure, one sigma bond and two pi bonds make up the triple link between carbon and nitrogen, which is a powerful and stable covalent bond.

Steps involved in HCN lewis structure:

1. Count the Valence Electrons:

Find out how many valence electrons each atom in the molecule has to find the HCN lewis structure.

The valence electron for hydrogen (H) is one.

There are 4 valence electrons in carbon (C).

There are 5 valence electrons in nitrogen (N).

For HCN, there are a total of 10 valence electrons (1 + 4 + 5 = 10).

2. Central Metal Atom:

Due to the fact that carbon can create numerous bonds while hydrogen can only form one, carbon serves as the core atom in the HCN Lewis structure.

3. Distribute Electrons:

Start by connecting the hydrogen and carbon with a pair of electrons (a bond). Out of the 10 available electrons, two are used in the HCN lewis structure. To complete the atoms’ valence shells, distribute the final 8 electrons among them. Only two electrons can fit in the valence shell of hydrogen. Nitrogen contains six valence electrons, compared to four for carbon. Check to see if each atom (except hydrogen) has an octet of electrons surrounding it after all the valence electrons have been distributed. Both nitrogen and carbon have 8 electrons (4 bond pairs), respectively.

4. Move the Electron Pair inward:

Just to make the carbon atom stable in HCN lewis structure, move the pair of electrons from nitrogen into an inward position towards carbon. The octet rule states that every atom (apart from hydrogen) must have eight electrons surrounding it. Each carbon atom and nitrogen atom in this structure is surrounded by 8 electrons.

5. Formal Charges:

To create the most stable HCN Lewis structure, determine the formal charges for each atom. This is how the formal charge is determined:

Formal Charge: (Number of Bonds + Number of Lone Pair Electrons) – Valence Electrons

To lessen the formal charge, make sure that each atom’s formal charge is as close to zero as possible. This completes the hydrogen cyanide (HCN) Lewis structure.

HCN Synthesis:

Due to its severe toxicity and potential for death, hydrogen cyanide (HCN) should only be synthesized by qualified individuals under the proper safety controls in a controlled laboratory setting. The following techniques are used to create hydrogen cyanide:

1. Andrussow Process:

This is the approach used in industry the most frequently to create HCN. It includes the high-temperature (1200 oC) reaction of ammonia (NH3) and methane (CH4) with oxygen over a platinum (Pt) or rhodium (Rh) catalyst. Because of how exothermic the reaction is, a lot of heat is produced. In order to create hydrocyanic acid (HCN (aq)), which is employed in a number of industrial operations, the resultant HCN gas is then absorbed in water.

2. Shawinigan Process:

In this procedure, ammonia, air, and natural gas—which contains methane—react over a catalyst. Similar to the Andrussow method, but with methane coming from natural gas instead of coal.

3. Laboratory Synthesis:

A cyanide salt, such as sodium cyanide, or a strong acid, such as hydrochloric acid, can be used to create hydrogen cyanide in a laboratory setting. Usually, this technique is applied on a small scale for certain investigations or reactions. Due to their toxicity, these substances must be handled with the utmost care.

Important Safety Considerations:

It is crucial to stress that HCN synthesis should only ever be carried out in expert and controlled laboratory settings and never as a casual or amateur experiment due to the significant risks connected with it.

  • Hydrogen cyanide is a deadly and very toxic substance.
  • All HCN synthesis should be carried out in a fume hood or a well-ventilated location with the necessary safety apparatus because even minor exposures to HCN gas can be lethal.
  • Proper protective clothing, such as lab coats, safety goggles, and gloves, should always be worn.
  • Employees who are involved in the synthesis of HCN should receive training in handling dangerous chemicals and have access to safety supplies, including eyewash stations and showers.

3 thoughts on “HCN Lewis Structure (in 5 steps): Amazing Guide”

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