Dinitrogen dihydride has the chemical formula of N2H2. This compound is most commonly known as diazene or diimide. It is a yellowish-colored gas having both cis and trans isomers. It can be prepared from the decarboxylation of azodicarboxylic acid ( (NCOOH)2 ).
Also, the application of air or H2O2 leads to oxidation of hydrazine ( N2H4, a colorless flammable liquid ) which results in the formation of N2H2.
Below is the chemical equation of preparation of Dinitrogen Dihydride/Diazene/Diimide
(NCOOH)2 ——> (NH)2 + 2 CO2
It melts at 193K and has a molar mass of 30.03 g/mol. It has a density of around 1.2 g/cc. Azo and diazo groups are substituents from diazene.
N2H2 has a lot of uses in organic synthesis. For example, it helps in the hydrogenation of alkenes and alkynes. Other than this, it also aids in the selective reduction of branched acyclic hydrocarbons.
When atomic elements come together to form molecular composition due to attraction and form certain types of bonds, the process is known as chemical bonding.
This is one of the most noteworthy chemical phenomena since it helps us understand the science behind atomic attraction and also the cause behind the occurrence of several chemical reactions.
Not only this, the nature of chemical bonding can help students of chemistry decipher various chemical and physical properties exhibited by different kinds of molecules and ions.
The valence shell electrons usually take part in bond formation and play important role in bonding. We are going to discuss this in detail in the upcoming sections where we will deal with the several methods and theories to grasp the bonding type in N2H2.
A Brief Intro
The nature of chemical bonding happening inside a molecular structure is a crucial chapter of chemistry. One of the initial strategies to understand chemical bonding is to draw the Lewis Structure of any given molecule.
Lewis Structure is a 2D diagrammatic representation of a molecular or an ionic structure that helps us decipher the type of bond formation and gives us a simple overview of electronic arrangement.
Let us find out the Lewis Structure of Dinitrogen dihydride, N2H2.
Lewis Structure of N2H2
The first step towards sketching the Lewis Structure of any molecule is to understand the concept of valency and calculation of valence electrons.
Valency is defined as the combining capacity of an atom for bond formation. This is indicated usually by the number of electrons in the outermost shell, also known as the valence shell.
Elements belonging to the same periodic table group will have the same number of valence electrons.
In the case of N2H2, a single molecule has two atoms of nitrogen and two atoms of hydrogen.
Let us look at the periodic table.
Nitrogen belongs to group 15 and has 5 valence electrons.
Hydrogen belongs to group 1 and has 1 valence electron.
Total number of valence electrons in N2H2 = 5*2 + 1*2 = 12.
Now, we have to identify the central atom in the molecule.
Here, we can see the Pauling Electronegativity chart. The general rule is to consider the element having the least electronegativity value as the central atom.
But an exception to this rule is the hydrogen atom which prefers to sit outside.
So, our rough sketch looks like this:
In Lewis Structure, we use the electron dot notations, i.e., we denote the valence shell electrons of the constituent atoms via dot symbols.
Now, here comes the octet fulfillment or the octet rule.
Octet rule: Do you know that the main group elements in the periodic table have a tendency to have eight valence electrons during bond formation? This tendency comes from the octet configuration of the noble gas elements present like Neon, Argon, etc.
Exception: Hydrogen tends to fulfill 2 electrons in its outer shell since it follows a Helium configuration.
Here, in the dinitrogen dihydride molecule, as we can see above, both the hydrogen atoms have attained He configuration. One N atom has eight electrons whereas the other one has only 6.
To fulfill the octet of the other N atom, we will have the Lewis Structure modified as:
Now, we have got the most suitable Lewis Structure for N2H2.
Lewis Structure has a lot of drawbacks even though it is one of the foremost and simplest methods to discuss chemical bonding.
For this, we come across VSEPR theory, short for Valence Shell Electron Pair Repulsion Theory which helps us determine the molecular geometry of any given structure.
What is VSEPR theory?
We are all aware of the fact that electrons are negatively charged particles that are present on the shells or orbitals surrounding atomic nuclei. Now, having negative charges make them repulsive since they are like-charged particles.
So, according to VSEPR theory, the repulsion that is created by the electron cloud surrounding the atomic nuclei needs to be minimized for maintaining stability and balance inside a molecule.
VSEPR model predicts the 3D molecular geometry or shape of a chemical compound.
So, how does an N2H2 molecule appear in 3D?
N2H2 Molecular Geometry
N2H2 molecule has two identical nitrogen atoms surrounded by two hydrogen atoms.
Let us, therefore, take any nitrogen atom from the available two atoms and consider it functioning as the central atom. This will help us decipher the 3D molecular shape easily.
Now, Valence Shell Electron Pair Repulsion theory suggests an AXE notation.
In AXnEx notation,
A stands for the central atom, here nitrogen acts as the central atom.
X stands for the number of surrounding atoms, here we have one hydrogen and one N-H group associated with the central N atom, hence ‘n’ stands for 2.
E stands for the number of lone pairs attached to the central atom, here we have one non-bonded pair on the central N, hence ‘x’ stands for 1.
Therefore, the N2H2 molecule has AX2E1 notation.
Now, we will check the VSEPR chart to find out the correct molecular geometry for diazene.
We can find out that for AX2E1 notation, the molecular geometry is bent and the bond angle is approximately 120 degrees.
The electron geometry will be about trigonal planar.
What is hybridization?
Hybridization, also known as orbital hybridization in chemistry, is an important chemical bonding concept introduced by Pauling. We already know that orbitals are defined to be mathematical probability offering us an idea of the presence of electrons in space.
We call them atomic orbitals and the wave functions of these atomic orbitals ( AOs ) like s, p, d, f, etc combine and fuse together to form several types of hybridized orbitals like sp, sp2, sp3, etc.
This process of redistribution of orbital energies of atoms towards hybrid orbitals is known as orbital hybridization.
Type of hybridization in Diazene ( N2H2 )
Now, that we have discussed what hybridization is and how important it is for the understanding of chemical bonding, we are going to talk about the type of hybridization in our given molecule N2H2.
Steric Number: Steric number is given by the formula:
Steric number = Number of atoms bonded to central atom inside a molecule + Number of lone pair of electrons attached to the central atom
Here, in a molecule of diazene, the nitrogen atom acts as the central atom.
If we look at the Lewis Structure, any N atom has two atoms attached to it: an N and an H atom via double and single bonds respectively.
The single bond has one sigma pair whereas the double bond has one sigma and one pi bond. The pi bond doesn’t take part in hybridization.
An N atom has one lone pair i.e. two lone electrons attached to it.
Therefore, steric number = 3.
Also, the formula for Hybridization is:
Here, V = 5, M = 1, C = 0, A = 0.
H = 3.
The hybridization of the central Nitrogen atom is sp2.
Molecular Orbital (MO) Diagram
In VBT, also known as Valence Bond Theory, we consider the fact that atomic orbitals ( AOs ) from the same individual atom can come together to form fusion into hybridized orbitals which overlap with hybridized orbitals formed by the combination of AOs from other individual atoms inside the molecule.
In quantum mechanics, we also come across the Molecular Orbital Theory or MOT. Here, valence or outermost shell electrons are shared between constituent atoms inside a given molecule to form molecular orbitals ( MOs ).
This is a famous and complex concept of chemical bonding.
Here, we deal with HOMO or Highest Occupied Molecular Orbital, LUMO or Lowest Unoccupied Molecular Orbital, anti-bonding, no-bonding, and bonding orbitals.
Apart from this, we also have Linear combination and United atom methodologies.
Below, we have a diagram explaining the MO of N2H2.
In this article, we have discussed the chemical bonding inside a diazene molecule. We have explained in detail the Lewis Structure, molecular geometry, hybridization, and MO diagram for the N2H2 molecule.