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Molecular orbital (MO) diagram for N2, N2+, N22-, N22+, N2-, and their bond order

If you are looking for the molecular orbital (MO) diagram of nitrogen (N2) then immediately stop scrolling. The good news is- you have hit the right spot.

This is by far the most comprehensive article you will find on the web, teaching you how to draw the Molecular orbital diagram of N2, what is its bond order and magnetic properties, etc.

Additionally, you will also find the MO diagrams of N2+, N2, N22+, and N22- all in this article.

Name of molecule

Nitrogen

Chemical formula

N2

Electronic configuration

1s2 2s2 2p3

Molecular orbital electronic configuration

(σ1s2)(σ*1s2)(σ2s2)(σ*2s2) (π2px2)(π2py2)(σ2pz2)

Number of electrons in bonding MOs

10

Number of electrons in anti-bonding MOs

4

Bond order

3

Paramagnetic or Diamagnetic?

Diamagnetic

 

How to draw the molecular orbital (MO) diagram of N2 with its bond order?

As per the molecular orbital theory (MOT) of chemical bonding, after bond formation, the individual atomic orbitals cease to exist. Rather, the atomic orbitals of constituent atoms combine to form a unique set of molecular orbitals (MOs).

The electrons of the participant atoms are thus held in these MOs, belonging to the entire molecule in unison.

The linear combination of atomic orbitals (LCAO) produces two types of molecular orbitals:

  • Bonding molecular orbitals
  • Anti-bonding molecular orbitals

The number of MOs produced is exactly equal to the number of atomic orbitals coming together.

A bonding molecular orbital is formed by the linear combination of two AOs in the same phase.

Contrarily, an antibonding molecular orbital is produced by the linear combination of two AOs in the opposite phase, counteracting the cohesive forces of the combining nuclei.

formation of bonding and antibonding Molecular orbital diagram (MO) for N2

This is why, a bonding MO always lies at a lower energy (greater stability) than the parent AOs while an antibonding MO occupies an energy level higher than that of parent AOs (higher instability).

The electrons are filled in these MOs following the three simple rules:

  1. Aufbau Principle: Electrons first occupy the lower energy orbitals followed by their placement in the higher energy molecular orbitals.
  2. Hund’s Rule: The incoming electrons are singly filled in the degenerate MOs before pairing occurs.
  3. Pauli Exclusion Principle: Two electrons placed in the same MO exhibit an opposite spin (clockwise and anticlockwise).

The different numbers of electrons present in the bonding and/or antibonding MOs of a molecule are represented in the form of an energy level diagram called the molecular orbital (MO) diagram.

The MO diagram in turn helps in predicting other useful properties of molecules such as their bond order, bond stability, magnetic behavior, etc.

Nitrogen (N2) is a homonuclear diatomic molecule. Two identical N-atoms combine to form an N2 molecule.

We can easily draw the Molecular orbital diagram of N2 following the steps given below.

Steps for drawing the molecular orbital (MO) diagram of N2 with its bond order

1. Write down the electronic configuration of N2 atoms

N2 is composed of two nitrogen (N) atoms.

The electronic configuration of each N-atom is 1s2 2s2 2px1 2py1 2pz1.

Usually, only the valence electrons are displayed in the MO diagram of a molecule, therefore, it is important to note that each N-atom contains 5 valence electrons.

2 N-atoms combined make a total of 14 electrons and 10 valence electrons in the N2 molecule.  

2. Determine whether the molecule is homonuclear or heteronuclear

N2 is a neutral molecule. It is homonuclear as it is formed by two atoms of the same element.

As per the rule of LCAO, the two 1s atomic orbitals of nitrogen overlap to produce two molecular orbitals i.e., a bonding molecular orbital (σ1s) and an antibonding molecular orbital (σ*1s).

Similarly, two 2s atomic orbitals combine to form two MOs, σ2s and σ*2s. Finally, the three 2p atomic orbitals from each N-atom overlap to produce six MOs including three bonding MOs (π2px, π2py, and σ2pz) and three anti-bonding MOs (π*2px, π*2py, and σ*2pz).

The MOs discussed above are located on the MO diagram in an increasing energy order.

Energy level diagram of N2

3. Fill the molecular orbitals of N2 with electrons following the energy and bonding principles

A total of 4 electrons are present in the 1s atomic orbitals of two nitrogen atoms. Therefore, as per the Aufbau principle, the first two electrons go in the lowest energy σ1s MO, and the remaining two are accommodated in σ*1s.

Similarly, the 4 electrons in the 2s atomic orbitals of nitrogen, are uniformly distributed between σ2s and σ*2s molecular orbitals of N2.

In contrast, there are a total of 3 + 3 = 6 electrons in the 2p atomic orbitals of two N-atoms.

2 out of the 6 electrons are first singly filled in the π2px and π2py MOs of N2 (Hund’s rule). These are then paired up in an opposite spin (Pauli Exclusion Principle).

The remaining 2 electrons (6 – 4 = 2) are finally situated as an electron pair in the σ2pz molecular orbital of N2. In this way, the 2p antibonding molecular orbitals of N2 stay entirely unoccupied. 

As a result, we have successfully drawn the Molecular orbital diagram of N2 as shown below.

Molecular orbital diagram (MO) of Nitrogen (N2) and it's bond order

Is N2 diamagnetic or paramagnetic?

N2 is a diamagnetic molecule as there are no unpaired electrons in its molecular orbital diagram.

Diamagnetic substances possess no permanent dipole moment value; therefore they get repelled by an external magnetic field.

Bond order of N2

The bond order formula is:

Bond order formula for N2

∴ Bond order = (Nb –Na)/2

  • Nb = Electrons present in the bonding MOs (Bonding electrons).

∴ Electrons in σ1s + σ2s + π2px + π2py + σ2pz = 2 + 2 + 2 + 2 + 2 = 10

  • Na= Electrons present in the anti-bonding MOs (Anti-bonding electrons).

∴ Electrons in σ*1s + σ*2s = 2 + 2 = 4

Bond order of N2 = (10 – 4)/2 = 6/2 = 3. 

A bond order of 3 implies that there is a triple covalent bond (N≡N) between two N-atoms in the N2 molecule.

A positive and significantly high bond order value also shows that the nitrogen molecule is extremely stable and it thus exists abundantly in Nature (76% of air is N2).

MO diagrams and bond orders of N2+, N2, N22+ and N22-  

N2+ represents a cation of nitrogen. It is a molecular ion formed by the loss of 1 valence electron from the nitrogen molecule.

This valence electron is removed from one of the three half-filled 2p orbitals of an individual N-atom. Upon N2+ formation, the σ2pz MO gets unpaired. As a result, N2+ is paramagnetic and its Molecular orbital diagram is as shown below:

∴ Bond order of N2+ = (Nb –Na)/2 = (9 – 4)/2 = 2.5  

MO electronic configuration of N2+: (σ1s2) (σ*1s2) (σ2s2) (σ*2s2) (π2px2) (π2py2) (σ2pz1)

Paramagnetic

N2+ Molecular orbital diagram (MO) and Bond order

Conversely, N22+ is formed by removing two electrons, one from a 2p AO of each N-atom. Therefore, both the electrons present in the σ2pz of N2 are removed resulting in the N22+ Molecular orbital diagram.

∴ Bond order of N22+ = (Nb –Na)/2 = (8 – 4)/2 = 2

MO electronic configuration of N22+: (σ1s2) (σ*1s2) (σ2s2) (σ*2s2) (π2px2) (π2py2)

Diamagnetic  

N22+ Molecular orbital diagram (MO) and Bond order

Contrarily, N2 is a negatively charged anion. 1 extra valence electron is gained by a N-atom. This extra electron singly fills π*2px in the Molecular orbital diagram of N2.

∴ Bond order of N2 = (Nb –Na)/2 = (10 – 5)/2 = 2.5

MO electronic configuration of N2: (σ1s2) (σ*1s2) (σ2s2) (σ*2s2) (π2px2) (π2py2) (σ2pz2) (π*2px1)

Paramagnetic

N2- Molecular orbital diagram (MO) and Bond order

Finally, N22- is formed when 2 extra valence electrons are gained in the 2p AOs, one by each parent N-atom. Thus, as per Hund’s rule, these 2 additional valence electrons singly occupy the π*2px and π*2py molecular orbitals in the Molecular orbital diagram of N22-, again a paramagnetic substance.

 ∴ Bond order of N22- = (Nb –Na)/2 = (10 –6)/2 = 2

MO electronic configuration of N22-: (σ1s2) (σ*1s2) (σ2s2) (σ*2s2) (π2px2) (π2py2) (σ2pz2) (π*2px1) (π*2py1)

Paramagnetic

N22- Molecular orbital diagram (MO) and Bond order

Stability and bond lengths of N2, N2+, N2, N22+ and N22-  

For the nitrogen family, the bond order increases as follows:

N22+ = N22- < N2 = N2+ < N2

Generally, bond order also signifies the strength of a bond. However, other factors such as the pattern in which electrons are filled in the respective bonding and antibonding MOs, may also affect overall bond strength and molecular stability.

Among the five species discussed above, the bond orders of N22+ and N22- are equal. Similarly, N2 and N2+ possess an identical bond order value. Still, N22- is less stable than N22+.

N22- contains unpaired electrons in the high-energy antibonding MOs (π*2px and π*2py) which leads to an overall destabilizing effect. However, no such electrons are present in the MO diagram of N22+ therefore, it is comparatively more stable.

A greater number of bonding electrons have a stabilizing effect while a greater number of antibonding electrons have a destabilizing effect.

Similarly, N2+ is relatively more stable than N2 considering a higher number of antibonding electrons in the latter.

Thus, on account of the factors discussed above, the N2 family is arranged in an ascending order of bond strength, energy, and stability as follows:

N22- < N22+ < N2 < N2+ < N2

On the other hand, bond order is inversely proportional to bond strength. The greater the bond strength, the closer the bonded atoms are to each other, i.e., a shorter bond length.

Therefore, the suspected bond lengths of the nitrogen family follow the reverse order:

N22- > N22+ > N2 > N2+ > N2

Also read:

FAQ

What is the molecular orbital diagram of N2?

The molecular orbital diagram of N2 is shown below.

MO diagram of N2

The MO electronic configuration of N2 is (σ1s2) (σ*1s2) (σ2s2) (σ*2s2) (π2px2) (π2py2) (σ2pz2).

There are no unpaired electrons in the above MO diagram, which means N2 is a diamagnetic substance.

What is the bond order of N2

The bond order of N2 is 3. There is a strong triple covalent bond between two identical N-atoms in the N2 molecule. The bond order is calculated from the MO diagram as follows:

Bond order = (Nb – Na)/2

  • Nb = number of electrons in bonding MOs = 10
  • Na = number of electrons in antibonding MOs = 4

Bond order = (10 – 4)/2

∴ Bond order = 6/2 = 3

Which molecular orbitals are called HOMO and LUMO in the MO diagram of N2

HOMO stands for highest occupied molecular orbital while LUMO denotes lowest unoccupied molecular orbital.

In the Molecular orbital diagram of N2, the bonding molecular orbital σ2pz lies at the highest energy level among those filled with electrons thus it is HOMO.

In contrast, the antibonding molecular orbitals π*2px and π*2py lie at the lowest energy level among the empty ones. Therefore, these are LUMO.

HOMO and LUMO molecular orbitals in the MO diagram of N2

What are the molecular orbital configurations of N2+, N22+, N2, N2and N22-?

MO electronic configuration of:

  • N2+ is (σ1s2)(σ*1s2)(σ2s2)(σ*2s2)(π2px2)(π2py2)(σ2pz1)
  • N22+ is (σ1s2)(σ*1s2)(σ2s2)(σ*2s2)(π2px2)(π2py2)
  • N2 is (σ1s2)(σ*1s2)(σ2s2)(σ*2s2)(π2px2)(π2py2)(σ2pz2)
  • N2 is (σ1s2) (σ*1s2) (σ2s2) (σ*2s2) (π2px2) (π2py2) (σ2pz2) (π*2px1)
  • N22- is (σ1s2) (σ*1s2) (σ2s2) (σ*2s2) (π2px2) (π2py2) (σ2pz2) (π*2px1) (π*2py1)

Why do the 2p pi-bonding molecular orbitals lie at a lower energy level as compared to the 2p sigma bonding MO in the MO diagram of N2 while it is the reverse in the MO diagrams of molecules such as O2 and F2?

A certain repulsive effect exists between σ*2s and σ2pz MOs in diatomic molecules having the sum of atomic number of elements = 14 or less than 14. This increases the energy of σ2pz above that of π2px and π2py.

Thus, the 2p pi-bonding MOs are situated below the 2p sigma-bonding MO in the MO diagrams of molecules such as Li2, Be2, B2, and up to N2.

However, the repulsive effect becomes insignificant in molecules of heavier elements, therefore in the Molecular orbital diagrams of O2, F2, Ne2, σ2pz lie below π2px and π2py.

In their respective Molecular orbital diagrams, how is the LUMO of N2different from that of N2

The 1 extra valence electron gained by N2 is placed in π*2px. Therefore π*2py is the only LUMO in N2 while π*2px and π*2py are two possibilities of lowest unoccupied molecular orbital in N2.

N2 vs N2- Molecular orbital diagram

Which of the following possesses the longest bond length?

N2 , N2 or N2+

Bond length is inversely related to the strength of a bond. Among N2, N2 and N2+, N2 possesses the highest bond order (3); therefore, it has the shortest bond length.

Contrarily, N2 and N2+ possess an equal bond order value (2.5), but still, N2+ is more stable than N2 due to a higher number of antibonding electrons in the latter. Therefore, N2 possesses the longest bond length out of all three.

Summary

  • Nitrogen (N2) is a homonuclear diatomic molecule. Two identical N-atoms combine to form N2.
  • The MO electronic configuration of N2 is (σ1s2)(σ*1s2)(σ2s2)(σ*2s2)(π2px2)(π2py2)(σ2pz2).
  • The absence of any unpaired electrons in the Molecular orbital diagram of N2 denotes it is a diamagnetic molecule.  
  • The bond order of N2 is 3 which means there is ideally a triple covalent bond between two N-atoms in the N2 molecule.
  • N2+, N2, N22+, and N22- are molecular ions formed by the loss or gain of electrons in the valence shell atomic orbitals of individual N-atoms.
  • The bond order follows the ascending pattern: N22- = N22+ < N2 = N2+ < N2 i.e., 2, 2.5, and 3 respectively.
  • N2+, N2, and N22- are paramagnetic while N22+ is diamagnetic in nature.
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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/

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