Q99P - Chemistry: Molecular Nature Of Matter And Change

Question

Draw orbital-energy splitting diagrams and use the spectrochemical series to show the orbital occupancy for each of the following (assuming that is a weak-field ligand):

$\mathbf{a}\mathbf{)}\mathbf{ }{\left[\mathrm{Cr}{\left(\mathrm{CN}\right)}_6\right]}^{\mathbf{3}\mathbf{-}}\mathbf{ }\mathbf{b}\mathbf{)}\mathbf{ }{\left[\mathrm{Rh}{\left(\mathrm{CO}\right)}_6\right]}^{\mathbf{3}\mathbf{+}}\mathbf{ }\mathbf{c}\mathbf{)}{\left[\mathrm{Co}{\left(\mathrm{OH}\right)}_6\right]}^{\mathbf{4}\mathbf{-}}$

Step-by-Step Solution

Answer

1. 3 d electrons
2. 6 d electrons
3. 7 d electrons

Crystal field splitting energy and spectrochemical series

The crystal field splitting energy $\left(\mathrm{\Delta }\right)$ represents the difference in energy between the two higher energy orbitals and the three lower energy orbitals; there are five orbitals which are splitted in two higher energy orbitals and three lower energy orbitals because of the electrostatic attractions between metal cation and ligands' negative charge.

 ${\mathrm{I}}^{-}<{\mathrm{Cl}}^{-}<{\mathrm{F}}^{-}<{\mathrm{OH}}^{-}<{\mathrm{H}}_2\mathrm{O}<{\mathrm{SCN}}^{-}<{\mathrm{NH}}_3<{\mathrm{en}}^{-}<{\mathrm{NO}}_2^{-}<{\mathrm{CN}}^{-}<\mathrm{CO}$

Spectrochemical series (from weak-field to strong-field ligands):

- the weaker the field is, the lower the splitting energy is $\left(\mathrm{\Delta }\right)$

- the stronger the field is, the higher the splitting energy is $\left(\mathrm{\Delta }\right)$ 

Orbital-energy splitting diagram

Orbital-energy splitting diagram

Orbital-energy splitting diagram