Hydrogen cyanide is a chemical compound with its chemical formula HCN. it is also known as prussic acid. It is a poisonous gas produced on an industrial scale. We will discuss its properties and many of you may also have doubts about whether HCN is polar or not. So, I will make you understand whether HCN is polar or not and the reason behind that.
So, is HCN polar or Nonpolar? HCN is a polar molecule because of the large electronegative difference between Nitrogen(3.04) and hydrogen(2.2) due to which the linear-shaped molecule has unequal sharing of charge and results in non zero dipole moment making the molecule polar.
HCN is acidic in nature. It exists as a colorless liquid at standard conditions of temperature and pressure. It is flammable in nature and an extremely poisonous liquid produced widely produced on an industrial scale.
This chemical compound has its molecular mass of 27.0253 g/mol. It can be calculated as below
Mol mass of HCN = 1* (Mol mass of H) + 1 * (Mol mass of C) + 1 * (Mol mass of N) = 1 + 12 + 14 =
The chemical composition of this chemical compound is covered by 1 carbon, 1 hydrogen, and 1 nitrogen atom.
Carbon is the central atom surrounded by nitrogen and hydrogen atoms on both sides such that it forms a linear shape structure.
The hydrogen has a valency of 1 (needs 1 electron more to get stable) and carbon has 4 valence electrons a requires 4 more to complete its octet and nitrogen has 5 valence electrons and needs 3 electrons more to complete its octet.
Accordingly, carbon and hydrogen share electrons of each other and forms a covalent bond(C-H) whereas carbon and nitrogen form a triple bond (C≡N) to share their three electrons with each other.
As a result, the molecule H-C≡N becomes stabilized.
If we check the electronegativity of its atoms, the electronegativity of carbon is 2.55, nitrogen is 3.04 and that of hydrogen is 2.2.
And nitrogen and carbon atoms are at extreme positions and have an appreciable difference in their electronegativity.
As a result, the nitrogen gains partial negative charge whereas the hydrogen gains partial positive charge. This creates positive and negative poles across the molecule making it a polar molecule.
Polar versus Nonpolar Molecules
The polar molecules are those molecules that have positive and negative poles generated across them.
The nonpolar molecules have no poles generated across it and have equal charge dispersed among its atoms.
The polar molecules have their dipole moment value equals to non zero. The distribution of charge among its atoms is non-uniform.
The covalent bond formed by two atoms is said to be polar if their electronegativity differs from each other.
This is because more electronegative atom pulls the bonded electron pair towards its side and gains partial negative charge and other atom gains partial positive charge.
The examples of polar molecules are HCl, OF2, etc. You can check the reason for the polarity of HCl.
The dipole moment of nonpolar molecules is always zero. Because in these molecules, the distribution of charge is always uniform across the entire molecule.
The covalent bond formed by two atoms is said to be nonpolar if the electronegativity of both atoms is equal.
The examples of nonpolar molecules are Hexane, BF3, etc. You can check out the reason for the non-polarity of BF3.
Why is HCN a Polar Molecule?
The molecule of HCN is polar as it contains the atoms (hydrogen, nitrogen, and carbon) that differs in their electronegativity.
The electronegativity of an atom is an important parameter to check if it is polar or not.
In simple words, the electronegativity of an atom is its power to pull the electron towards its side.
So, greater electronegative atom pulls bonded electron pair to its side with more influence and gives rise to charge imbalance.
As a result, greater electronegative atom gains partial negative charge due to more charge intensity on it.
The difference between the electronegativity of nitrogen and hydrogen is (3.04 -2.2= 0.84) which is sufficient to raise polarity in the HCN molecule.
The shape of this molecule is linear and has a net dipole towards nitrogen.
Apart from the electronegativity factor, the nitrogen is connected with carbon with a triple bond that also increases the intensity of charge on the nitrogen atom and makes the molecule polar.
Key Points to determine the polarity of a molecule
There exist several parameters that should be kept in mind while checking the polarity of a molecule. You should note down the below points and observe them
Electronegativity: If there is a covalent bond formed between two atoms differing in their electronegativity, then the higher electronegative atom pulls the electron slightly more towards its side.
As a result, the bond formed is polar. If there is a difference between the electronegativity of atoms involved in a molecule, the molecule formed is polar in nature.
The difference in electronegativity is directly proportional to the polarity of the molecule.
In the case of H-C≡N, Nitrogen is more electronegative than hydrogen and carbon become the negative pole.
Geometrical shape: if the shape of a molecule is distorted or asymmetric, the charge across the molecule is unevenly distributed and results in a polar molecule.
Whereas the symmetrically shaped molecule is nonpolar only if the electronegativity of atoms is equal. If it mismatches, the molecule can be polar.
Like in the case of HCN, although the shape of the molecule is symmetric (linear), the molecule is polar due to the difference in electronegativity of its atoms.
Below is the image of the geometrical structure of the HCN molecule.
Dipole Moment: the dipole of a molecule is the measure of its polarity. Greater the polarity of a molecule more is its polarity.
It is the product of charge on atoms and the distance between the centers of positive and negative charge.
D = Q* R
It is denoted by D. The dipole of the HCN molecule is 2.98 Debye. Debye is its SI.
Properties of HCN
- It exists as a colorless liquid at room temperature with an oily odor.
- It is poisonous and flammable in nature produced over a wide range from industries.
- It is acidic in nature and has an acidity of 9.21 PKA.
- The melting point of this substance is −13.29 °C or 8.08 °F, and its boiling point is 26 °C or 79 °F.
- At a temperature of 25 °C, its vapor pressure is 100 kPa.
- The polarity of HCN is 2.98 D.
- The molecular shape of HCN is linear.
Uses of HCN
- HCN is used in the preparation of acrylonitrile which is further used in the manufacturing of synthetic rubbers, acrylic fibers.
- It is also used in the production of plastics.
- HCN and compounds formed with this are useful for many chemical reactions. For example, itis used in the hardening of steel and iron.
- This compound is also used in the process of electroplating.