Q39E - Chemistry (OpenStax)

Question

Why is boron limited to a maximum coordination number of four in its compounds?

Step-by-Step Solution

Answer

Boron is limited to a maximum coordination number of four in its compounds because from the electron configuration, it is clear that a boron atomonly has the s and p orbitals and no d orbital. A maximum of four pairs of electrons can be present in these orbitals.

Step 1: Coordination number

The count of atoms/ions/moleculesthat a central atom/ion can hold in a particular complex is termed as the coordination number.It is evaluated by counting the neighboring atoms around a central atom.

 

Step 2: Reason for a maximum coordination number of four in boron compounds

Boron is limited to a coordination number of 4 because of its size. Its atomic number is 5 and its electron configuration is \({\rm{1}}{{\rm{s}}^{\rm{2}}}{\rm{2}}{{\rm{s}}^{\rm{2}}}{\rm{2}}{{\rm{p}}^{\rm{1}}}\). With a small number of protons and electrons, it has a very small radius. 

 

From the electron configuration, it is clear that borononly has the s and p orbitals and no d orbital. A maximum of four pairs of electrons can be present in these orbitals.

 

For these reasons, there can't be more than four atoms surrounding aboron atom.