What is the molecular orbital diagram for $B_{2}$ $B_2$ ?

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Answer 1 · 2015-01-27T03:25:50

Before we can draw a molecular orbital diagram for B₂, we must find the in-phase and out-of-phase overlap combinations for boron's atomic orbitals.

Then we rank them in order of increasing energy.

We can ignore the $1 s$ $1s$ orbitals, because they do not contain the valence electrons.

Each boron atom has one $2 s$ $2s$ and three $2 p$ $2p$ valence orbitals.

The $2 s$ $2s$ orbitals will overlap to form $2 s σ$ $2sσ$ and $2 s σ *$ $2sσ"*"$ orbitals.

The $2 p_{x}$ $2p_x$ orbitals can overlap end-on to form $2 p σ$ $2pσ$ and $2 p σ *$ $2pσ"*"$ orbitals.

The $2 p_{y}$ $2p_y$ and $2 p_{z}$ $2p_z$ orbitals can overlap side-on to form degenerate pairs of $2 p π$ $2pπ$ and $2 p π *$ $2pπ"*"$ orbitals.

The order of energies is $2sσ < 2sσ^✳ < 2pπ < 2pσ < 2pπ^✳ < 2pσ^✳$ .

We have three valence electrons from each B atom, so B₂ will have six valence electrons.

We use the Pauli Exclusion Principle and Hund's rule to fill the orbitals in an Aufbau process.

The molecular orbital diagram for B₂ then becomes

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The video below describes how to generate molecular orbital diagrams for B₂ and other diatomic molecules from Row 2 elements of the Periodic Table.

What is the molecular orbital diagram for B_2B2B_2?