Polar or nonpolar, is HCN?

Hydrogen cyanide is a chemical substance represented by the formula HCN. Also referred to as prussic acid. It is an industrially manufactured gas that is toxic. Many of you may also have doubts as to whether HCN is polar or not, which we will examine. Therefore, I shall explain whether or not HCN is polar and the rationale for such.

Is HCN therefore polar or nonpolar? HCN is a polar molecule due to the high electronegative difference between Nitrogen (3.04) and hydrogen (2.2), which results in unequal charge distribution and a nonzero dipole moment, which makes the molecule polar.

HCN is an acidic substance. It occurs as a colourless liquid under ordinary temperature and pressure conditions. It is naturally combustible and a very toxic liquid that is mass-produced on an industrial basis.

The molecular mass of this chemical compound is 27,0253 g/mol. It can be computed as follows:

Mol mass of HCN equals 1* (Mol mass of H) + 1* (Mol mass of C) + 1* (Mol mass of N) = 1 + 12 + 14 =

27 g/mol.

This chemical compound has one carbon, one hydrogen, and one nitrogen atoms.

Carbon is the core element surrounded on both sides by nitrogen and hydrogen atoms to form a linear structure.

Carbon has four valence electrons and needs four more to complete its octet, whereas nitrogen has five valence electrons and need three more to complete its octet.

Consequently, carbon and hydrogen share electrons and create a covalent link (C-H), whereas carbon and nitrogen form a triple bond (CN) to share three electrons.

Consequently, the molecule H-CN is stabilised.

Checking the electronegativity of its atoms reveals that carbon’s electronegativity is 2.55, nitrogen’s is 3.04, and hydrogen’s is 2.2.

In addition, nitrogen and carbon atoms occupy extreme locations and exhibit a significant variance in electronegativity.

Thus, nitrogen acquires a partial negative charge whereas hydrogen acquires a partial positive charge. This results in the formation of positive and negative poles across the molecule, making it polar.

Polar versus Nonpolar Molecules

Polar molecules are those that generate positive and negative poles across their surface.

Nonpolar molecules having no produced poles and an equal distribution of charge among their atoms.

The dipole moment value of polar molecules is greater than zero. Non-uniform distribution of charge among its atoms.

If the electronegativity of the two atoms forming the covalent bond differ, then the covalent bond is polar.

This occurs because the more electronegative atom attracts the bound electron pair to its side and acquires partial negative charge, whilst the other atom acquires partial positive charge.

Examples of polar molecules are HCl, OF2, etc. You can investigate the cause of HCl’s polarity.

Nonpolar molecules have a dipole moment that is always zero. Because the distribution of charge in these molecules is always uniform across the entire molecule.

If the electronegativity of both atoms is equivalent, then the covalent bond formed between them is nonpolar.

Examples of nonpolar molecules are hexane and BF3. You can investigate the cause of BF3’s non-polarity.

Why does HCN possess polarity?

HCN is a polar molecule because its constituent atoms (hydrogen, nitrogen, and carbon) have differing electronegativity.

The electronegativity of an atom is a crucial criterion for determining whether or not it is polar.

In straightforward terms, the electronegativity of an atom is its ability to attract electrons to its side.

Therefore, a more electronegative atom attracts bound electron pairs to its side with greater force, resulting in a charge imbalance.

As a result, a more electronegative atom acquires a portion of a negative charge as its charge intensity increases.

The difference in electronegativity between nitrogen and hydrogen is sufficient to increase polarity in the HCN molecule (3.04 -2.2 = 0.84).

This molecule has a linear structure with a net dipole towards nitrogen.

In addition to the electronegativity component, the nitrogen is coupled to carbon by a triple bond, which raises the charge intensity on the nitrogen atom and polarises the molecule.

Key Elements to Determine a Molecule’s Polarity

When evaluating the polarity of a molecule, numerous parameters must be taken into consideration. You should record the following points and adhere to them

Electronegativity: When two atoms with varying electronegativity create a covalent bond, the more electronegative atom pulls the electron somewhat more towards its side.

Consequently, the resulting bond is polar. If there is a variation in the electronegativity of the atoms that comprise a molecule, the molecule is polar.

Polarity of the molecule is exactly proportional to the difference in electronegativity.

Nitrogen is more electronegative than hydrogen in the case of H-CN, hence carbon becomes the negative pole.

If the form of a molecule is twisted or asymmetric, the charge is unevenly distributed across the molecule, resulting in a polar molecule.

In contrast, a molecule with a symmetrical form is nonpolar only if the electronegativity of its atoms is identical. If there is a mismatch, the molecule may be polar.

Similar to HCN, although the molecule’s structure is symmetric (linear), it is polar due to the difference in electronegativity between its atoms.

The figure below depicts the geometric structure of the HCN molecule.

The polarity of a molecule is determined by its dipole moment. The more a molecule’s polarity, the greater its polarity.

It is the product of atomic charge and the distance between positive and negative charge centres.

D = Q* R

It is represented by D. The HCN molecule has a dipole of 2.98 Debye. Debye serves as its SI.

Qualities of HCN

It exists as an odourless, colourless liquid at ambient temperature.

It is toxic and combustible by nature and is manufactured in a variety of industries.

It is naturally acidic, with an acidity of 9.21 PKA.

This substance has a melting point of 13.29 °C or 8.08 °F and a boiling temperature of 26 °C or 79 °F.

At 25 degrees Celsius, its vapour pressure is 100 kPa.

HCN has a polarity of 2.98 D.

HCN molecules have a linear form.

Applications of HCN

HCN is used to produce acrylonitrile, which is then utilised in the production of synthetic rubbers and acrylic fibres.

It is also used to manufacture polymers.

HCN and its compounds are important in numerous chemical processes. For instance, it is used to harden steel and iron.

This chemical is also utilised in the electroplating process.

Read more: Polar or nonpolar, H2S?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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