HCN Molecular Geometry - Science Education and Tutorials

Hydrogen cyanide(HCN) has the composition of one cyanide species and one hydrogen atom. What is the molecular geometry of hydrogen cyanide?. Drawing and predicting the HCN molecular geometry is very easy by following the given method. Here in this post, we described step by step to construct HCN molecular geometry. carbon, nitrogen, and hydrogen come from the 14th, 15 th, and 1st family groups in the periodic table. Carbon, nitrogen, and hydrogen have four, five, and one valence electrons respectively.

Table of Contents

Key Points To Consider When drawing The HCN Molecular Geometry

A three-step approach for drawing the HCN molecular can be used. The first step is to sketch the molecular geometry of the HCN molecule, to calculate the lone pairs of the electron in the central carbon atom; the second step is to calculate the HCN hybridization, and the third step is to give perfect notation for the HCN molecular geometry.

The HCN molecular geometry is a diagram that illustrates the number of valence electrons and bond electron pairs in the HCN molecule in a specific geometric manner. The geometry of the HCN molecule can then be predicted using the Valence Shell Electron Pair Repulsion Theory (VSEPR Theory) and molecular hybridization theory, which states that molecules will choose the HCN geometrical shape in which the electrons have from one another in the specific molecular structure.

Finally, you must add their bond polarities characteristics to compute the strength of the one H-CN single bonds (dipole moment properties of the HCN molecular geometry). One hydrogen-carbon single bond and carbon-nitrogen triple bond in the hydrogen cyanide(HCN), for example, are polarised toward the more electronegative value nitrogen atom of cyanide species, and because (H-CN) single bonds have the same size and polarity, their sum is nonzero due to the HCN molecule’s bond dipole moment due to pulling the electron cloud to the two side of linear molecular geometry, and the HCN molecule is classified as a polar molecule.

The molecule of hydrogen cyanide(with linear shape HCN molecular geometry) is tilted at 180 degrees bond angle of H-CN. It has a difference in electronegativity values between carbon and hydrogen atoms, with carbon’s pull the electron cloud being greater than hydrogen’s. But bond polarity of H-Br is not canceled to each other in the linear molecular geometry. As a result, it has a nonzero permanent dipole moment in its molecular structure. The HBr molecule has a nonzero dipole moment due to an unequal charge distribution of negative and positive charges in the linear molecular geometry.

Overview: HCN electron and molecular geometry

According to the VSEPR theory, the HCN molecule ion possesses linear molecular geometry. Because the center atom, carbon, has one H-CN single bond with the one hydrogen atom surrounding it. The H-CN bond angle is 180 degrees in the linear HBr molecular geometry. The HCN molecule has a linear molecular geometry shape because it contains one hydrogen atom in the one terminal and another nitrogen in the opposite terminal with one lone pairs of electrons.

There is one H-CN single bond at the HCN molecular geometry. After linking the one hydrogen atom and no lone pairs of electrons on the carbon atom in the linear molecular form, it maintains the linear-shaped structure. In the HCN molecular geometry, the H-CN single bond has stayed in the one terminal and one lone pair of electrons on the nitrogen terminal atom of the linear molecule.

The center carbon atom of HCN has no lone pair of electrons, resulting in linear HCN electron geometry. However, the molecular geometry of HCN looks linear-shaped and has one lone pair of electrons on the terminal nitrogen of the HCN geometry. It’s the HCN molecule’s slight asymmetrical geometry. As a result, the HCN molecule is slightly polar.

How to find HCN hybridization and molecular geometry

Calculating lone pairs of electrons on carbon in the HCN geometry:

1.Determine the number of lone pairs of electrons in the core carbon atom of the HCN Lewis structure. Because the lone pairs of electrons on the carbon atom are mostly responsible for the HCN molecule geometry planar, we need to calculate out how many there are on the central carbon atom of the HCN Lewis structure.

Use the formula below to find the lone pair on the carbon atom of the HCN molecule.
L.P(C) = V.E(C) – N.A(H-CN)

Lone pair on the central carbon atom in HCN = L.P(C)
The core central carbon atom’s valence electron in HCN = V.E(C)
Number of H-CN bond = N.A (H-CN)
calculation for carbon atom lone pair in HCN molecule.

For instance of HCN, the central carbon atom has four electrons in its outermost valence shell, four H-CN single bonds connection. This gives a total of four connections.

As a result of this, L.P(C) = (4–4)=0

The lone pair of electrons in the carbon atom of the HCN molecule is zero.

Calculating lone pairs of electrons on nitrogen in the HCN geometry:

1.Determine the number of lone pairs of electrons in the terminal nitrogen atom of the HCN Lewis structure. Because the lone pairs of electrons on the nitrogen atom are mostly responsible for the HCN molecule geometry planar, we need to calculate out how many there are on the terminal nitrogen atom of the HCN Lewis structure.

Use the formula below to find the lone pair on the nitrogen atom of the HCN molecule.
L.P(N) = V.E(N) – N.A(H-CN)

Lone pair on the central nitrogen atom in HCN = L.P(N)
The core central nitrogen atom’s valence electron in HCN = V.E(N)
Number of H-CN bond (around nitrogen atom) = N.A (H-CN)
calculation for nitrogen atom lone pair in HCN molecule.

For instance of HCN, the terminal nitrogen atom has five electrons in its outermost valence shell, three H-CN single bonds connection. This gives a total of three connections.

As a result of this, L.P(N) = (5–3)=2

The lone pair of electrons in the terminal nitrogen atom of the HCN molecule is two (one lone pair).

Calculating lone pair of electrons on hydrogen in the HBr geometry:

Finding lone pair of electrons for the terminal hydrogen atom is similar to the central carbon atom. We use the following formula as given below

Use the formula below to find the lone pair on the hydrogen atom of the HCN molecule.
L.P(H) = V.E(H) – N.A(H-CN)

Lone pair on the terminal hydrogen atom in HCN = L.P(H)
Terminal hydrogen atom’s valence electron in HCN= V.E(H)
Number of H-CN bonds = N.A ( H-CN)
calculation for hydrogen atom lone pair in HCN molecule.

For instance of HCN, their terminal atoms, hydrogen, have one electron in its outermost valence shell, one H-CN single bond connection. This gives a total of one H-CN single bond connection. But we are considering only one connection for the calculation.

As a result of this, L.P(H) = (1 –1)=0

The lone pair of electrons in the hydrogen atom of the HCN molecule is zero. One hydrogen atom is connected with the central carbon atom.

In the HCN electron geometry structure, the lone pairs on the central carbon atom is zero, lone pairs of electrons in the hydrogen atom have zero. One hydrogen atom has no lone pairs of electrons.

It means there are no lone pairs of electrons in the core carbon atom. No lone pair of electrons on the central carbon atom is responsible for the linear of HCN molecular geometry. But in the structure hydrogen atom is polarised sidewise in their linear geometry.

The one lone pairs of electrons are placed at another side of a nitrogen atom in the HCN geometry. Because the hydrogen atom is a lower electronegative value as compared with other atoms in the HCN molecule. One hydrogen atom is polarized towards the sidewise in the HCN structure.

But in reality, the HCN has one lone pair of electrons in its structure. This makes the HCN more asymmetrical in the structure of the molecule. Because there is electric repulsion between bond pairs and lone pairs.

But some sort of interaction is there between hydrogen empty hole and lone pairs of electrons of carbon of another HCN molecule. Here, hydrogen of one molecule acts as an acceptor and nitrogen of the other molecule as a donor. This is called hydrogen bonding between the two HCN molecules. This is one of the main intermolecular forces in HCN.

But in the central, the carbon atom has no lone pair of electrons and these lone pair electrons are placed in the two terminal of linear geometry.

Calculate the number of molecular hybridizations of the HCN molecule

What is HCN hybridization? This is a very fundamental question in the field of molecular chemistry. All the molecules are made of atoms. In chemistry, atoms are the fundamental particles. There are four different types of orbitals in chemistry. They are named s, p, d, and f orbitals.

The entire periodic table arrangement is based on these orbital theories. Atoms in the periodic table are classified as follows:

s- block elements
p- block elements
d-block elements
f-block elements
Atoms are classified in the periodic table

HCN molecule is made of one carbon, nitrogen, and hydrogen atom. The hydrogen, nitrogen and carbon atoms have s and p orbitals. But hydrogen atom has only s orbital in the ground state. Hydrogen comes as the first element in the periodic table. The carbon atom also belongs to the carbon family group. But it falls as the first element in the periodic table. Nitrogen belongs to nitrogen family group.

When these atoms combine to form the HCN molecule, its atomic orbitals are mixed and form unique molecular orbitals due to hybridization.

How do you find the HCN molecule’s hybridization? We must now determine the molecular hybridization number of HCN.

The formula of HCN molecular hybridization is as follows:
No. Hyb of HCN= N.A(H-CN bond) + L.P(C)
No. Hy of HCN = the number of hybridizations of HCN
Number of H-CN bonds = N.A (H-CN bonds)
Lone pair on the central carbon atom = L.P(C)
Calculation for hybridization number for HCN molecule

In the HCN molecule, carbon is a core central atom with one hydrogen atom connected to it. It has no lone pair of electrons on carbon. The number of HCN hybridizations (No. Hyb of HCN) can then be estimated using the formula below.

No. Hyb of HCN= 0+2=2

The HCN molecule ion hybridization is two. The carbon, nitrogen, and hydrogen atoms have s and p orbitals. The sp hybridization of the HCN molecule is formed when one s orbital and one p orbitals join together to form the HCN molecular orbital.

Molecular Geometry Notation for HCN Molecule :

Determine the form of HCN molecular geometry using VSEPR theory. The AXN technique is commonly used when the VSEPR theory is used to calculate the shape of the HCN molecule.

The AXN notation of HCN molecule is as follows:
The central carbon atom in the HCN molecule is denoted by the letter A.
The bound pairs (four H-CN bonds) of electrons to the core carbon atom are represented by X.
The lone pairs of electrons on the central carbon atom are denoted by the letter N.
Notation for HCN molecular geometry

We know that HCN is the core carbon atom, with four electron pair bound (one H-CN) and no lone pair of electrons on central carbon atom. The general molecular geometry formula for HCN is AX4.

According to the VSEPR theory, if the HCN molecule ion has an AX4 generic formula, the molecular geometry and electron geometry will be linear-shaped forms.

Name of Molecule	Hydrogen cyanide
Chemical molecular formula	HCN
Molecular geometry of HCN	linear
Electron geometry of HCN	linear
Hybridization of HCN	sp
Bond angle (H-CN)	180º degree
Total Valence electron for HCN	10
The formal charge of HCN on carbon	0

Summary:

In this post, we discussed the method to construct HCN molecular geometry, the method to find the lone pairs of electrons in the central HCN atom, HCN hybridization, and HCN molecular notation. Need to remember that, if you follow the above-said method, you can construct the HCN molecular structure very easily.