Who hasn’t heard of NO2, also known as Nitrogen Dioxide?
It is one of the most prevalent reddish-brown gaseous molecules. It can be cooled and compacted into a brown-yellow liquid for transport and storage.
NO2 is a major air pollutant and a very harmful, poisonous chemical molecule that belongs to the oxides of nitrogen.
This compound has bleaching and sterilising applications.
It finds use in the tobacco and explosives industries. NO2 is an intermediary in the production of HNO3 acid and an oxidizer for rocket and spacecraft fuels.
Below are the laboratory procedures for preparing Nitrogen Dioxide.
Lewis Structure
A Brief Overview
A positively charged nucleus is surrounded by electrons in their shells, generating a negatively charged cloud within an atom.
Valence electrons are the electrons in the outermost shell that determine the valency.
Lewis Structure is a diagrammatic representation of a molecule’s constituent atoms and the position and arrangement of their electrons to form bonds and lone pairs.
This is a limited theory on the basis of chemical bonds and electronic structure, yet it provides a straightforward perspective on the synthesis of any molecular composition.
Let’s discuss how to draw the Lewis Structure for nitrogen dioxide ( NO2 ).
NO2’s Lewis Structure
The molecule of nitrogen dioxide contains one nitrogen atom and two oxygen atoms.
Examining the periodic table.
Nitrogen is a member of group 15 (or group 5) and has the atomic number 7, hence its valency is 5. Oxygen is a member of group 16 (or group 6) with an atomic number of 8 and a valency of 6.
Total number of valence electrons in NO2 = 5 + 6*2
= 17.
To determine which atom will serve as the centre atom, we must now consult Pauling’s Electronegativity chart.
Nitrogen is the less electronegative of the two elements, hence it will serve as the centre atom.
Thus, we have positioned the nitrogen atom in the centre, flanked by two O atoms.
Now, using dot structures, we shall encircle the atoms with their valence electrons.
Here, we have adhered to the octet rule.
Octet Rule
Do you know that the valence shells of the elements in the major groups of the periodic table tend to form an eight-electron configuration similar to that of noble gases?
This is known as the octet rule and is a crucial notion for sketching a molecule’s most probable Lewis Structure.
Reconsider the diagram. We have already achieved the Neon configuration for the two O atoms.
Now, the Nitrogen atom is surrounded by only five electrons, and the whole number of valence electrons has already been used.
To achieve a near octet configuration for the Nitrogen atom, we will move two electrons from one O atom and form a double bond.
Here we go.
Nitrogen now contains seven electrons and has achieved a configuration close to an octet.
Formal Demand
Let us examine the formal fee.
Formal Fee for O ( in a single bond with N )
= 6 – 0.5*2 – 6 = 6 – 1 – 6 = -1.
Formal Fee for O ( in a double bond with N )
= 6 – 0.5*4 – 4 = 6 – 2 – 4 = 0.
The formal charge of the central nitrogen atom.
= 5 – 0.5*6 – 1 = 5 – 3 – 1 = 1.
If we now calculate the entire formal fees, we obtain a net result of zero.
As a result, the molecule is neutral and the elements have the lowest attainable formal charge values.
Consequently, the most appropriate Lewis Structure of NO2 is:
Molecular Geometry
Let we examine the disadvantages of Lewis Structure:
It is only capable of providing a 2D depiction, not a 3D one.
Lewis Structure can only describe the arrangement of electrons, not their distribution.
It is only capable of identifying the type of bond formation but is unable to expound on its formation.
Herein lies the function of VSEPR theory:
VSEPR concept
VSEPR refers to the model of Valence Shell Electron Pair Repulsion.
According to this idea, because electrons carry similar charges (‘-‘), they must feel repulsion, the degree of which differs between coupled and lone pair electrons.
To build a stable or balanced polyatomic molecule or ionic structure, this repulsive force must therefore be minimised.
Thus, VSEPR facilitates the prediction of the 3D molecular geometry or form of a molecule, as well as the bond angles.
What is NO2’s Molecular Geometry?
In the VSEPR model, the AXnEx notation is utilised.
A represents the centre atom, which is nitrogen in this case ( N ).
X represents the surrounding atoms, which in this case are two O atoms.
n represents the number of atoms surrounding the centre element, and its value is 2.
E represents unpaired electrons (often a lone pair), while x represents the number.
Here, since there is only one electron, we will count it as 1.
We employ the AX2E1 notation.
VSEPR graph:
NO2 has a bent molecular geometry, and the angle is around 120 degrees.
But there are exceptions in this case. NO2 has two Bond Pairs and one lone electron.
The nitrite ion NO2- consists of 2 Bond Pairs and 1 Lone Pair of electrons.
There is also a curved structure, however since the order of repulsion strength is LP-LP > LP-BP > BP-BP, the bond angle order is as follows:
NO2+ > NO2 > NO2-.
Consequently, the bond angle of NO2 is around 134 degrees. The bond length is around 1.20.
Hybridization
Orbital Hybridization
Are you aware that an electron’s wave function can be used to characterise it?
Atomic orbitals, the mathematical probability functions indicating the existence of electrons in any region of space, are familiar to us.
When the wave functions of atomic orbitals mix or fuse, hybrid orbitals occur; this process is known as orbital hybridization.
Combination of NO2
The single bond N-O consists of one sigma bond, whereas the double bond N=O consists of one sigma bond plus one pi bond. Pi bond is not involved in hybridization.
Now, because NO2 has 17 valence electrons, it is an odd-electron system. For single electron species, we must adhere to the following rule:
If the oxidation status of the central atom is determined to be positive, the electron will participate in the hybridization process; otherwise, it will not.
In nitrogen dioxide,
Steric No = 2 sigma plus one solitary electron.
The core nitrogen is less electronegative than the central oxygen. Therefore, N has a positive charge.
The oxidation state is therefore determined to be positive, and the lone electron will participate in hybridization.
steric no = 2 + 1 = 3. Consequently, NO2 hybridization is sp2.
NO2 Polarization
What exactly is Polarity?
Polarity is an essential chemical topic. Polarity is a feature of every chemical composition that determines whether the molecule is polar or non-polar. This is dependent on the chemical bonding nature, which impacts the form and geometry.
A diatomic homogeneous molecule that comprises of similar atoms always results in zero dipole moment and consequently non-polar.
However, a heterogeneous polyatomic molecule has a number of atomic components with varied electronegativity values. This creates partial charges on atoms, which, if not neutralised, produce polar compounds.
In addition, the irregularity and asymmetry of molecules, aided by lone pairs and bonds, result in polarity due to the unequal distribution of charges.
How can NO2 become a polar molecule?
The electronegativity of nitrogen is 3.04 and that of oxygen is 3.44.
This indicates a difference in electronegativity between the two atomic elements. Although the difference is relatively small, NO2 is in fact a polar molecule due to its asymmetrically bent molecular structure, which causes a net dipole moment.
Additionally, you should read this essay on the Polarity of NO2 for more information.
Molecular Orbital (MO) Diagram
Explanation
Electrons possess both particle and wave properties. The Molecular Orbital hypothesis is a quantum mechanics idea that aims to explain chemical bonding within any molecule.
According to this theory, valence electrons can be shared among all constituent atoms, and atomic orbitals from distinct atoms combine to generate molecular orbitals ( MOs ).
Anti-bonding orbitals, non-bonding orbitals, and bonding orbitals will be discussed in this section. In addition, we have the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) concepts ( Lowest Unoccupied Molecular Orbital).
MO Diagram for NO2
Let us examine the electrical structure of both N and O.
N: 1s2 2s2 2p3
O: 1s2 2s2 2p4 ( we have two O atoms in NO2 )
The six electrons present in the 1s orbital do not participate in bonding; hence, they will serve as non-bonding orbitals.
The two 1s2 electrons of the Nitrogen atom participate in the 2s MO. Each oxygen atom contributes two lone pair.
The remaining electrons in N and O’s p orbitals create 2px, 2py, 2pz, and *2s.
Conclusion
NO2 is one of the most prevalent diatomic heteronuclear compounds. In this article, we have examined in depth the nature of the molecule’s chemical bonds.
We hope you have gone through the procedures of building a perfect Lewis structure, the use of VSEPR theory notations to compute bond angles and predict molecular geometry, the hybridization process, polarity, and the molecular orbital idea of bonding.
Enjoy!
Read more: Structure, Molecular Geometry, and Hybridization of CH2O
