Molecular orbital (MO) diagram for Ne2, Ne2+, Ne22+, and their bond order

Does Ne₂ exist? Is it a stable molecule? If so, what is its bond order, and how to calculate it? If all these questions intrigue you, then you must be looking for the molecular orbital (MO) diagram of Ne₂. The good news is – you have hit the right spot.

In this article, you will find a step-by-step guide on drawing the Molecular orbital diagrams of Ne₂, Ne₂⁺, and Ne₂²⁺. We will also teach you to write the MO electronic configuration of each of the above species, calculate their bond orders, and determine their magnetic properties.

So, for all that and much more continue reading the article.

How to draw the molecular orbital (MO) diagram of Ne₂ 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.

The formula Ne₂ represents a homonuclear diatomic molecule i.e., a molecule containing two atoms from the same element, in this case, a Noble gas element, neon (Ne) from Group VIII A (or 18) of the Periodic Table.

You can easily draw the Molecular orbital diagram of Ne₂ following the simple steps given below.

Steps for drawing the molecular orbital (MO) diagram of Ne₂ with its bond order

1. Write down the electronic configuration of Ne₂ atoms

Ne₂ comprises two identical neon (Ne) atoms.

The electronic configuration of each Ne-atom is 1s² 2s² 2p⁶.

Usually, only the valence electrons are displayed in the MO diagram of a molecule, therefore, it is important to note that each Ne-atom contains 8 valence electrons.

2 Ne-atoms combined make a total of 2(10) = 20 electrons and 2(8) = 16 valence electrons to be filled in the Molecular orbital diagram of Ne₂.

2. Determine whether the molecule is homonuclear or heteronuclear

Ne₂ 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 neon 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 Ne-atom overlap to produce six MOs including three bonding MOs (σ2p_z, π2p_x, and π2p_y) 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 Ne₂ with electrons following the energy and bonding principles

A total of 4 electrons are present in the 1s atomic orbitals of two neon 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 neon, are uniformly distributed between σ2s and σ*2s molecular orbitals of Ne₂.

In contrast, there are a total of 6 + 6 = 12 electrons in the 2p atomic orbitals of two Ne-atoms.

These electrons are filled in the Molecular orbital diagram of Ne₂ as follows:

• 2 electrons occupy σ2p_z as an electron pair.
• The next 2 electrons are first singly filled in the π2p_x and π2p_y MOs (Hund’s rule). These are then paired up in an opposite spin (Pauli Exclusion Principle).
• The 2p antibonding MOs (π*2p_x and π*2p_y) are then filled with a total of 4 electrons, 2 each in the same manner.
• The last 2 electrons occupy the highest energy level σ*2p_z.

In this way, we obtain the correct Molecular orbital diagram of Ne₂, completely filled with electrons, as shown below.

As per the above diagram, the Molecular orbital electronic configuration of Ne₂ is-

(σ1s²) (σ*1s²) (σ2s²) (σ*2s²) (σ2p_z²) (π2p_x²) (π2p_y²) (π*2p_x²) (π*2p_y²) (σ*2p_z²)

Is Ne₂ diamagnetic or paramagnetic?

Ne₂ 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 Ne₂

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 + σ2p_z + π2p_x + π2p_y = 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 + σ*2p_z = 2 + 2 + 2 + 2 +2 = 10

⇒ Bond order of Ne₂ = (10 – 10)/2 = 0/2 = 0. 

A bond order of zero means Ne₂ is an extremely unstable molecule. It is rather a hypothetical (imaginary) molecule that does not exist in real life.

Neon (Ne) is a Noble gas element, inert in nature. It does not react with itself or other elements to gain stability; rather it is very stable on its own possessing a full outer shell electronic configuration i.e., a complete octet (8 valence electrons).  

MO diagrams and bond orders of Ne₂⁺ and Ne₂²⁺

Ne₂⁺ represents a cation of the neon dimer. It is a molecular ion formed by the loss of 1 valence electron from Ne₂.  

This valence electron is removed from one of the three 2p orbitals of an individual Ne-atom.

20 – 1 results in a total of 19 electrons to be filled in the Molecular orbital diagram of Ne₂⁺.

Thus, upon Ne₂⁺ formation, the electron present in the highest energy σ*2p_z MO gets unpaired. As a result, Ne₂⁺ is paramagnetic and its Molecular orbital diagram is as shown below:

∴ Bond order of Ne₂⁺ = (N_b –N_a)/2 = (10 – 9)/2 = 0.5  

Molecular orbital electronic configuration of Ne₂⁺: (σ1s²) (σ^*1s²) (σ2s²) (σ^*2s²) (σ2p_z²) (π2p_x²) (π2p_y²) (π*2p_x²) (π*2p_y²) (σ^*2p_z¹).   

⇒ Paramagnetic

On the other hand, Ne₂²⁺ is formed by removing two electrons, one from a 2p AO of each Ne-atom.

20-2  results in a total of 18 electrons to be filled in the MO diagram of Ne₂²⁺.

Therefore, both the electrons present in σ*2p_z MO of Ne₂ get unpaired, producing the Ne₂²⁺ MO diagram.

The absence of any unpaired electron reveals the diamagnetic nature of Ne₂²⁺.

∴ Bond order of Ne₂²⁺ = (N_b –N_a)/2 = (10 – 8)/2 = 1

Molecular orbital electronic configuration of Ne₂²⁺: (σ1s²) (σ^*1s²) (σ2s²) (σ^*2s²) (σ2p_z²) (π2p_x²) (π2p_y²) (π*2p_x²) (π*2p_y²).

⇒ Diamagnetic

Bond strength, stability, and bond lengths of Ne₂, Ne₂⁺, and Ne₂²⁺

Both Ne₂⁺ and Ne₂²⁺ ions possess bond order values greater than zero. This means these molecular ions are relatively more stable than the parent molecule i.e., Ne₂. Ne₂⁺ and Ne₂²⁺ thus exist in real life. However, Ne₂²⁺ is more stable than Ne₂⁺.

The bond order signifies the strength of a bond. Therefore, for the Ne₂ family, the bond strength increases as follows:

Ne₂ < Ne₂⁺ < Ne₂²⁺

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

Therefore, the suspected bond lengths of the Ne₂ family follow the reverse order:

Ne₂ > Ne₂⁺ > Ne₂²⁺

Also read:

• Molecular orbital diagram (MO) for O2+, O2-, O22+, O22-, O2, 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 NF+, NF, NF-, 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

• Ne₂ represents a homonuclear diatomic molecule, containing two identical Ne-atoms.
• The MO electronic configuration of Ne₂ is (σ1s²) (σ*1s²) (σ2s²) (σ*2s²) (σ2p_z²) (π2p_x²) (π2p_y²) (π*2p_x²) (π*2p_y²) (σ*2p_z²).
• The absence of any unpaired electron in the Molecular orbital diagram of Ne₂ predicts its diamagnetic nature.   
• The bond order of Ne₂ is zero, which means Ne₂ is extremely unstable and does not exist in real.
• Ne₂⁺ and Ne₂²⁺ are molecular ions formed by the loss of electrons from the valence shell atomic orbitals of individual Ne-atoms.
• The bond order follows the ascending pattern: Ne₂ < Ne₂⁺ < Ne₂²⁺ i.e., 0, 0.5, and 1 respectively.
• Ne₂⁺ is paramagnetic while both Ne₂ and Ne₂²⁺ are diamagnetic in nature.