Molecular Orbital Diagram for O2 Molecule, Molecular Orbital Diagram for N2 Molecule

 

Molecular orbital Diagram for O₂ molecule

The electronic configuration of oxygen (Z=8) is 1s², 2s², 2p⁴ (1s^↿⇂, 2s^↿⇂, 2p_x^↿⇂ 2p_y^↿ 2p_z^↿) Thus there are five atomic orbitals with 8 electrons in each oxygen atom. The two participating oxygen atoms contribute a total 16 valence electrons. These five atomic orbitals of both oxygen atoms combine to form ten molecular orbitals as shown in molecular orbital energy diagram.

 

Two p-atomic orbitals (one from each oxygen) atom combine to form two molecular orbitals, the bonding molecular orbital σ2p_x and antibonding molecular orbital σ*2p_x. The other four p-atomic orbitals (two from each oxygen) atom combines to give four molecular orbitals, two bonding molecular orbitals i.e. π2p_y and π2p_z, while two antibonding molecular orbitals i.e. π*2p_y and π*2p_z. The electron filling in these molecular orbitals follows Aufbau, Pauli exclusion principle and Hund’s rule.

Out of eight electrons, six go to bonding molecular orbitals and two to the antibonding molecular orbitals. As electrons are also present in antibonding molecular orbitals, so weak bonds will be formed.

Bond Order

Bond order of O₂ molecules is determined as

N_b – N_a/2 = 10–6 /2 = 2 (Double bond, O=O)

OR 

We can calculate bond order by considering electrons in p-orbitals as

N_b – N_a/2 = 6–2 /2 = 2

As the bond order in Oxygen is 2 so two bonds i.e. double bonds formed between two oxygen atoms (O=O). 

Reason of Paramagnetic Nature of O₂ molecule

Since there are two unpaired electrons in degenerate anti-bonding molecular orbital (π*2p_y and π*2p_z), O₂ molecule is paramagnetic in nature.

 

molecular orbital configuration with increasing energy order

 

𝜎1s^↿⇂ < 𝜎*1s^↿⇂ < 𝜎2s^↿⇂ < 𝜎*2s^↿⇂ < < 𝜎 2px^↿⇂ < 𝜋2py^↿⇂ = 𝜋2pz^↿⇂ < 𝜋*2py^↿ = 𝜋*2pz^↿ < 𝜋*2px

Summary of MO Diagram of O₂

Given element  – Oxygen

Atomic number of Oxygen = 7

Electronic configuration of O atom = 1s^↿⇂, 2s^↿⇂, 2p_x^↿⇂ 2p_y^↿ 2p_z^↿

Total number of electrons in Oxygen molecule = 16 (8 by each O)

Electronic configuration of O₂ =

𝜎1s^↿⇂ < 𝜎*1s^↿⇂ < 𝜎2s^↿⇂ < 𝜎*2s^↿⇂ < < 𝜎 2px^↿⇂ < 𝜋2py^↿⇂ = 𝜋2pz^↿⇂ < 𝜋*2py^↿ = 𝜋*2pz^↿ < 𝜋*2px

Bond order of O₂ molecules = N_b – N_a/2 = 10–6 /2 = 2 (Double bond, O=O)

Paramagnetic nature = Two unpaired electrons in anti-bonding orbitals, hence O₂ is paramagnetic. 

Molecular orbital Diagram for N₂ molecule

The electronic configuration of nitrogen (Z=7) is 1s², 2s², 2p³ (1s^↿⇂, 2s^↿⇂, 2p_x^↿ 2p_y^↿ 2p_z^↿) Thus there are five atomic orbitals with 7 electrons in each nitrogen atom. The two participating nitrogen atoms contribute a total 14 valence electrons. These five atomic orbitals of both nitrogen atoms combine to form ten molecular orbitals as shown in molecular orbital energy diagram.

 

Two p-atomic orbitals (one from each nitrogen) atom combine to form two molecular orbitals, the bonding molecular orbital σ2p_x and antibonding molecular orbital σ*2p_x. The other four p-atomic orbitals (two from each nitrogen) atom combines to give four molecular orbitals, two bonding molecular orbitals i.e. π2p_y and π2p_z, while two antibonding molecular orbitals i.e. π*2p_y and π*2p_z. The electron filling in these molecular orbitals follows Aufbau, Pauli exclusion principle and Hund’s rule.

 

Out of seven electrons, five go to bonding molecular orbitals and two to the antibonding molecular orbitals. All six electrons of p-orbitals go to bonding molecular orbitals, so strong bonds will be formed.

Bond order

Bond order of N₂ molecules is determined as

Bond order = N_b – N_a/2 = 10 – 4/2 = 3

 

OR

Bond order = N_b – N_a/2 = 6 – 0/2 = 3

 

As the bond order in nitrogen is 3 so three bonds i.e. triple bonds formed between two nitrogen atoms (N≡N). 

 

Reason of Diamagnetic Nature of N₂ molecule

Since there is no unpaired electron in any of the molecular orbitals of nitrogen molecule, hence N₂ molecule is diamagnetic in nature.

 

molecular orbital configuration with increasing energy order

𝜎1s < 𝜎*1s < 𝜎2s < 𝜎*2s < 𝜋2py = 𝜋2pz < 𝜎 2px < 𝜋*2py = 𝜋*2pz < 𝜋2px

 

Summary of MO Diagram of N₂

Given element  – nitrogen

Atomic number of nitrogen = 7

Electronic configuration of N atom = 1s^↿⇂, 2s^↿⇂, 2p_x^↿ 2p_y^↿ 2p_z^↿

Total number of electrons in nitrogen molecule = 14 (7 by each N)

Electronic configuration of N₂ =

𝜎1s < 𝜎*1s < 𝜎2s < 𝜎*2s < 𝜋2py = 𝜋2pz < 𝜎 2px < 𝜋*2py = 𝜋*2pz < 𝜋2px

Bond order of N₂ molecules = N_b – N_a/2 = 10–4 /2 = 3 (Triple bond, N≡N)

Diamagnetic nature = No unpaired electrons in any orbitals, hence N₂ is diamagnetic.