Molecular orbital (MO) diagram for NF+, NF, NF-, and their Bond order

If you are curious to know how to draw the MO diagram of NF, then this article is for you.

In this article, we will teach you the tips and tricks of drawing the Molecular orbital diagrams of NF, NF⁺, and NF^– and calculating their bond orders, predicting their bonding principles, molecular stability, and magnetic behavior.

So without any further delay, learn all of that and much more by continuing to read the article. 

How to draw the molecular orbital (MO) diagram of NF 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 (BMO) is formed by the linear combination of two AOs in the same phase.

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

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 displayed schematically on an energy level diagram called the molecular orbital (MO) diagram.

NF is a heteronuclear diatomic molecule i.e., a molecule containing two atoms from more than one type of element, in this case, nitrogen (N) and fluorine (F).

Follow the steps given below and draw the molecular orbital diagram of NF with us.

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

1. Write down the electronic configuration of NF atoms

NF is made up of one atom of nitrogen (N) and one fluorine (F) atom.

The electronic configuration of a N-atom is 1s² 2s² 2p³.

The electronic configuration of a F-atom is 1s² 2s² 2p⁵.

7 electrons of nitrogen and 9 electrons of fluorine make a total of 7 + 9 = 16 electrons available to be filled in the MO diagram of the NF molecule.

Usually, only the valence electrons are displayed in the MO diagram of a molecule, therefore, it is important to note that there are 5 + 7 = 12 valence electrons in the NF molecular orbital diagram.

2. Determine whether the molecule is homonuclear or heteronuclear

As discussed above, NF is a heteronuclear molecule. This implies that in the MO diagram of NF, the individual atomic orbitals of the N-atom and the F-atom do not lie at the same energy level.

Fluorine is a more electronegative element than nitrogen. Also, it bears a higher effective nuclear charge than the latter. Therefore, the AOs of the F-atom lie at a lower energy level than the corresponding AOs of the N-atom, as shown below. 

As per the rule of LCAO, the 1s atomic orbital of the F-atom overlaps with the 1s atomic orbital of the N-atom 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 six 2p atomic orbitals, three from each of the two atoms, combine to produce six MOs including three bonding MOs (π2p_x, π2p_y, and, σ2p_z) and three anti-bonding MOs (π*2p_x, π*2p_y, and σ*2p_z).

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

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

A total of 4 electrons are present in the 1s atomic orbitals of the N-atom and the F-atom. 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 from the 2s atomic orbitals, are uniformly distributed between σ2s and σ*2s molecular orbitals of NF.

Next, there are a total of 8 electrons in the 2p atomic orbitals of the N-atom and the F-atom. The first two electrons singly fill the π2p_x and π2p_y MOs (as per Hund’s rule) and then pairing occurs in an opposite spin (as per Pauli Exclusion Principle).

The next two electrons are subsequently filled as an electron pair in π2p_z MO. The last two electrons then singly occupy the π*2p_x and π*2p_y antibonding MOs, as shown below.

As per the molecular orbital diagram (MO) of NF successfully drawn above, the MO electronic configuration of NF is (σ1s²) (σ*1s²) (σ2s²) (σ*2s²) (π2p_x²) (π2p_y²) (σ2p_z²) (π*2p_x¹) (π*2p_y¹).

Is NF diamagnetic or paramagnetic?

The presence of two unpaired electrons in the Molecular orbital diagram of NF confirms its paramagnetic nature.

Possessing unpaired electrons, paramagnetic substances when exposed to an external magnetic field, experience a magnetic pull and behave like magnets themselves.  

Bond order of NF

The bond order formula is:

∴ Bond order = (N_b –N_a)/2

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

∴ Electrons in σ1s + σ2s + π2p_x + π2p_y + σ2p_z = 2 + 2 + 2 + 2 + 2 = 10

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

∴ Electrons in σ*1s + σ*2s + π*2p_x + π*2p_y = 2 + 2 + 1 + 1 = 6

⇒ Bond order of NF = (10 – 6)/2 = 4/2 = 2. 

Bond order > 0 implies that NF is a stable molecule.

Additionally, a bond order value of 2 means that there is a double covalent bond (N=F) between the nitrogen and fluorine atoms in the NF molecule.

MO diagrams and bond orders of NF⁺ and NF^–

NF⁺ represents a cation of nitrogen monofluoride.  It is formed when either the N-atom or the F-atom loses an electron from its valence shell to change into a positively charged ion. In either case, there are a total of 16 -1 = 15 electrons available to be filled in the MO diagram.

Thus, the electron present in the π*2p_y MO of NF is removed producing the NF⁺ molecular orbital diagram, as shown below.

One unpaired electron still present makes NF⁺ a paramagnetic molecular species.

∴ Bond order of NF⁺ = (N_b –N_a)/2 = (10 –5)/2 = 2.5

Molecular orbital electronic configuration of NF⁺: (σ1s²) (σ^*1s²) (σ2s²) (σ^*2s²) (π2p_x²) (π2p_y²) (σ2p_z²) (π*2p_x¹).

⇒ Paramagnetic

In contrast, NF^– is a negatively charged molecular ion, produced as a result of the strongly electronegative F-atom gaining an extra valence electron to complete its octet.

This results in a total of 16 + 1 = 17 electrons available to be filled in the Molecular orbital diagram of NF^–. The extra electron is paired up in the π*2p_x molecular orbital, as shown below.

One unpaired electron in the above MO diagram suggests the paramagnetic nature of NF^– in conjunction with NF and NF⁺.

∴ Bond order of NF^– = (N_b –N_a)/2 = (10 –7)/2 = 1.5

Molecular orbital electronic configuration of NF^–: (σ1s²) (σ^*1s²) (σ2s²) (σ^*2s²) (π2p_x²) (π2p_y²) (σ2p_z²) (π*2p_x²) (π*2p_y¹).

⇒ Paramagnetic 

The bond order also signifies the strength and stability of a bond. Therefore, for the NF family, the bond strength increases in the order:

NF^– < NF < NF⁺

However, an increasing bond order in turn means a decreasing bond length. Therefore, the bond lengths of the NF family follow the reverse order:

NF^– > NF > NF⁺

Also read:

• Molecular orbital diagram (MO) for Ne2, Ne2+, Ne22+, and Bond order
• Molecular orbital diagram (MO) for C2, C2-, C2+, C22+, C22-, and Bond order
• Molecular orbital diagram (MO) for He2+, He2, He22+, He22-, He2-, and Bond order
• Molecular orbital diagram (MO) for H2, H2-, H2+, H22-, H22+, and Bond order
• Molecular orbital diagram (MO) for Li2, Li2+, Li2-, Li22-, Li22+, and Bond order
• Molecular orbital diagram (MO) for Be2, Be2+, Be22-, Be2-, Be22+, and Bond order
• Molecular orbital diagram (MO) for B2, B2+, B22-, B2-, B22+, and Bond order
• Molecular orbital diagram (MO) for N2, N2+, N22-, N22+, N2-, and Bond order
• Molecular orbital diagram (MO) for F2, F2+, F2-, F22+, F22-, and Bond order
• Molecular orbital diagram (MO) for O2+, O2-, O22+, O22-, O2, and Bond order
• Molecular orbital diagram (MO) for NO, NO+, NO-, and Bond order
• H2O Molecular orbital diagram (MO), Bond order
• HF Molecular orbital diagram (MO), Bond order

FAQ

Summary

• Nitrogen monofluoride (NF) is a heteronuclear diatomic molecule, containing two atoms from two different elements.
• The Molecular orbital electronic configuration of NF is (σ1s²)(σ^*1s²)(σ2s²)(σ^*2s²) (π2p_x²)(π2p_y²) (σ2p_z²)(π^*2p_x¹)(π^*2p_y¹)
• The presence of two unpaired electrons in the π2p antibonding MOs of NF means it is paramagnetic in nature.
• The bond order of NF is 2, which implies that it is a stable molecule, containing a double covalent bond between the N-atom and the F-atom.
• NF⁺ and NF^– are molecular ions formed by the loss and gain of an electron, respectively in the valence shell atomic orbitals of constituent atoms.
• The bond order follows the ascending pattern: NF^– < NF < NF⁺ e., 1.5, 2, and 2.5 respectively.
• Both NF⁺ and NF^– are paramagnetic molecular ions.