Nitrosyl chloride (NOCl) Lewis dot structure, molecular geometry or shape, electron geometry, bond angle, formal charges, hybridization, polar vs nonpolar
Let’s talk about NOCl in this article. NOCl is the chemical formula for nitrosyl chloride, a strong oxidizing agent that exists as a yellowish gas at room temperature and pressure. The colorless aqua regia (HNO3: HCl in the ratio 1:3) turns yellow to orange-red within seconds due to the formation of NOCl and NO2.
If you are interested in knowing the chemistry behind NOCl, including how to draw its Lewis structure, what is its molecular geometry or shape, electron geometry, bond angle, formal charges, hybridization, polarity, etc., then this article is for you.
So without any further delay, let’s start reading!
The Lewis structure of NOCl consists of three different elemental atoms. A nitrogen (N) atom is present at the center of the molecule. It is bonded to an oxygen (O) atom via a double covalent bond and to an atom of chlorine (Cl) via a single covalent bond. A lone pair of electrons is also present at the central N-atom.
In this way, there are a total of 3 electron density regions around the central N-atom in the Lewis structure of NOCl containing 2 bonded atoms and 1 lone pair.
Drawing the Lewis structure of NOCl is not a difficult task at all. So, grab a paper and pencil and draw this Lewis structure with us following the simple steps given below.
Steps for drawing the Lewis dot structure of NOCl
1. Count the total valence electrons in NOCl
The Lewis dot structure of a molecule is a simplified representation of all the valence electrons present in it. Therefore, the very first step while drawing the Lewis structure of NOCl is to calculate the total valence electrons present in its concerned elemental atoms.
There are three different types of atoms present in a nitrosyl chloride (NOCl) molecule. We can find the valence electrons present in each element by identifying them in the Periodic Table.
Nitrogen (N) is present in group V-A of the Periodic Table, so it has a total of 5 valence electrons. Oxygen (O) is situated in group VI-A, so it has a total of 6 valence electrons. Conversely, chlorine (Cl) is a halogen present in group VII-A which denotes it has a total of 7 valence electrons in each atom.
∴ The NOCl molecule comprises 1 nitrogen atom, 1 oxygen atom, and 1 atom of chlorine, respectively. So, the total valence electrons available for drawing the Lewis dot structure of NOCl = 5 + 6 + 7 = 18 valence electrons.
2. Choose the central atom
Electronegativity is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond. Thus, the least electronegative atom is most likely to share its electrons with other atoms in its surroundings.
As Nitrogen (N) is less electronegative as compared to both oxygen (O) and chlorine (Cl) in the NOCl molecule. Therefore, nitrogen is placed at the center of the NOCl Lewis structure while both O and Cl atoms occupy terminal positions, as shown in the figure below.
3. Connect outer atoms with the central atom
In this step, we need to connect the outer atoms with the central atom of the Lewis structure using single straight lines. As O and Cl atoms are the outer atoms in NOCl so the O atom, as well as the Cl atom, are joined to the central N atom using straight lines, as shown below.
Each straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons. There are a total of 2 straight lines in the above structure which means 2(2) = 4 valence electrons are used so far, out of the 18 initially available.
Total valence electrons available – electrons used till step 3 = 18-4 = 14 valence electrons.
This means we still have 14 valence electrons available to be accommodated in the Lewis dot structure of NOCl.
4. Complete the octet of outer atoms
One oxygen (O) and one chlorine (Cl) are the outer atoms in the NOCl Lewis structure.
Both atoms require a total of 8 valence electrons in order to achieve a stable octet electronic configuration.
The N-O bond at the center represents 2 electrons. Thus, oxygen requires 6 more electrons to complete its octet. These 6 valence electrons are placed as 3 lone pairs around the oxygen atom.
Similarly, the N-Cl bond represents 2 electrons which means the Cl atom also require 6 more electrons to achieve a stable octet configuration. These 6 electrons are thus placed as 3 lone pairs around the Cl atom, as shown below.
5. Complete the octet of the central atom and make a covalent bond if necessary
Total valence electrons used till step 4 = 2 single bonds + electrons placed around O-atom + electrons placed around the Cl-atom = 2(2) + 6 + 6 = 16 valence electrons.
Total valence electrons available – electrons used till step 4 = 18 – 16 = 2 valence electrons.
So these 2 valence electrons are consequently placed as a lone pair on the central N-atom in NOCl.
But a problem that stays is that 2 single bonds and 1 lone pair around the central N-atom make a total of 6 valence electrons. This means it is still deficient of 2 more electrons in order to have a complete octet.
But don’t worry because this problem can be solved by converting a lone pair present on the outer O-atom into a bond pair shared between the central N and the outer O-atom, as shown below.
Cl cannot share its lone pair to form the extra bond because it is deficient in only 1 electron to attain a complete octet, so it can only form a single bond with the adjacent atom. Contrarily, oxygen has 6 valence electrons; it can form a double bond to complete its octet.
Now, if you look at the structure above, you see the central N-atom has a complete octet having 1 double bond + 1 single bond + 1 lone pair. Also, the octet of the outer O-atom is complete with 1 double bond and 2 lone pairs. Similarly, the Cl-atom has a complete octet with 1 single bond + 3 lone pairs.
As a final step, we just need to check the stability of the above Lewis structure and we can do so by using the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The fewer formal charges present on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
What are the electron and molecular geometry of NOCl?
The ideal electron geometry of the nitrosyl chloride (NOCl) molecule is trigonal planar. However, it is due to a lone pair of electrons present on the central nitrogen atom that the molecule adopts a bent shape or molecular geometry, different from its ideal electron geometry.
Molecular geometry of NOCl
The shape or molecular geometry of the nitrosyl chloride (NOCl) molecule is bent. It is also known as an angular or V-shape. The presence of a lone pair of electrons on the central N-atom in NOCl leads to lone pair-bond pair electronic repulsions in addition to the N=O and N-Cl bond pair-bond pair repulsive effect. This strong repulsive effect pushes the bonded oxygen and chlorine atoms away from the center.
The N=O and N-Cl bonds tilt toward one another and away from the lone pair at the top. Consequently, the molecule obtains a bent shape.
It must be noted that the molecular geometry or shape of a molecule depends on the different number of lone pairs and bond pairs around the central atom.
Contrarily, its ideal electronic geometry just depends upon the total number of electron density regions or electron domains (lone pairs and bond pairs inclusive) around the central atom.
Now let us see how this concept applies to the NOCl molecule.
Electron geometry of NOCl
According to the valence shell electron pair repulsion (VSEPR) concept of chemical bonding, the ideal electronic geometry of a molecule containing 3 regions of electron density around the central atom is trigonal planar.
The N=O double bond is considered one region of electron density. The N=O bond along with an N-Cl bond and a lone pair of electrons represent make a total of 3 electron density regions around the central N-atom in NOCl. Thus, its electron geometry is trigonal planar.
A more straightforward way of determining the shape and geometry of a molecule is to use the AXN method.
AXN is a simple formula to represent the number of atoms bonded to the central atom in a molecule and the number of lone pairs present on it.
It is used to predict the shape and geometry of a molecule based on the VSEPR concept.
AXN notation for the NOCl molecule
A in the AXN formula represents the central atom. In NOCl, nitrogen (N) acts as the central atom, so A = N.
X denotes the atoms bonded to the central atom. 1 O and 1 Cl atom are bonded to the central N atom in the NOCl molecule; thus, X=2.
N stands for the lone pairs present on the central atom. As 1 lone pair is present on central nitrogen in NOCl, thus N=1.
So, the AXN generic formula for the NOCl molecule is AX2N1.
Now have a quick look at the VSEPR chart given below to identify where you find AX2N1.
The VSEPR chart confirms that molecules with an AX2N1 generic formula have a bent or V-shape while their ideal electron geometry is trigonal planar, as we already noted down for the NOCl molecule.
Hybridization of NOCl
The central N atom is sp2 hybridized in the NOCl molecule.
The electronic configuration of nitrogen (N) is 1s2 2s2 2p3.
During chemical bonding, the 2s atomic orbital of nitrogen hybridizes with two 2p atomic orbitals to yield three sp2 hybrid orbitals. One of these three sp2 hybrid orbitals contains paired electrons which are situated as a lone pair on the central N-atom in NOCl.
The other two sp2 hybrid orbitals contain a single electron each. These two sp2 hybrid orbitals of nitrogen overlap with the sp2 hybrid orbital of oxygen and the p orbital of chlorine to form the N-O and the N-Cl sigma (σ) bonds, respectively.
The unhybridized p-orbitals of nitrogen and oxygen form the N=O pi (π) bond by p-p overlap.
A short trick for finding the hybridization present in a molecule is to memorize the table given below. You can find the steric number of a molecule and use that against this table to find its hybridization.
The steric number of central nitrogen (N) in NOCl is 3 so it has sp2 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The NOCl bond angle
The ideal bond angle of a trigonal planar molecule is 120°. However, it is due to a lone pair repulsive effect and consequently the distortion present in the molecular shape that the O=N-Cl bond angle decreases from the ideal 120° to 113° in NOCl.
There are also two different bond lengths in the NOCl molecule. The N=O bond length is 114 pm, while the N-Cl bond length is 198 pm, as shown in the figure below.
A double bond is stronger than a single bond, and thus, it exhibits a shorter bond length than the length of a single bond.
Both chlorine (E.N = 3.16) and oxygen (E.N = 3.44) atoms are more electronegative than the central nitrogen (E.N = 3.04) in NOCl.
An electronegativity difference of 0.12 units exists between the N and Cl atoms in an N-Cl bond, while an electronegativity difference of 0.40 units exists between the N and O atoms in the N=O bond.
Thus, both N-Cl and N=O bonds are polar in the NOCl molecule. These polar bonds possess a specific dipole moment value (symbol μ).
It is due to the asymmetric bent of the molecule that the dipole moments of the N-Cl and the N=O bonds do not get canceled in NOCl. Rather their polarity effect adds up. The electron cloud stays non-uniformly distributed in the molecule overall; hence, NOCl is polar with net μ =1.9 D.
What is the Lewis structure for nitrosyl chloride (NOCl)?
The Lewis structure of NOCl displays a total of 18 valence electrons, e., 18/2 = 9 electron pairs.
Out of these 9 electron pairs, there are 3 bond pairs and 6 lone pairs of electrons.
2 bond pairs are shared between the central N-atom and the outer O-atom to form the N=O bond.
1 bond pair is shared between the central N-atom and the outer Cl-atom to form the N-Cl bond.
1 lone pair of electrons is present on the central N-atom, while 2 and 3 lone pairs are present on the outer O and Cl atoms, respectively.
Why is N the central atom for NOCl Lewis structure?
Nitrogen is less electronegative than both oxygen and chlorine. So nitrogen is chosen as the central atom in the NOCl Lewis structure.
A less electronegative atom is less likely to attract other electrons and thus possesses a greater tendency to share its electrons with the other bonded atoms.
What is the molecular geometry of NOCl?
The molecular geometry or shape of NOCl is bent, V-shaped, or angular.
Why NOCl has a different shape or molecular geometry from its ideal electronic geometry?
The molecular geometry or shape of NOCl is different from its ideal electronic geometry, i.e., bent vs. trigonal planar.
A lone pair of electrons present on the central N-atom in NOCl leads to lone pair-bond pair repulsions that distort the shape and geometry of the molecule.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
Topblogtenz is a website dedicated to providing informative and engaging content related to the field of chemistry and science. We aim to make complex subjects, like chemistry, approachable and enjoyable for everyone.
