Explain why \[G{{d}^{3+}}\] is colourless.

Hint: Gd is the symbol of Gadolinium element present in periodic table with the atomic number 66. It is a ductile, shiny and a soft metal present in the lanthanide group of the periodic chart. It has the ability to not get tarnish in dry air but get an oxide film in moist air. It reacts slowly with water but gets dissolved in acid.


Complete solution:
The electronic configuration of gadolinium is \[[Xe]4{{f}^{7}}5{{d}^{1}}6{{s}^{2}}\]. The electronic configuration of \[G{{d}^{3+}}\]ion is \[[Xe]4{{f}^{7}}\]. As the element is losing its three electrons to make \[G{{d}^{3+}}\]ion so the oxidation state will be +3. The ion \[G{{d}^{3+}}\]is a stable ion because on observing its electronic configuration we can see that its 4f orbital is half filled. And we have read that the fully filled and half filled orbitals are stable. The half filled orbital is stable because of the symmetry present in it and the exchange of energy as the electrons have occupied different positions in the orbitals of the sub shell so they can exchange their positions. As it has attained stability so it does not allow f-f transition and does not absorb the radiation present in the visible region. So \[G{{d}^{3+}}\]ion is a colourless ion.


Note:Gadolinium is used in microwave application and in colour television too in the form of phosphorus. The alloy formed from gadolinium is used in manufacturing of video recorders and electronic gadgets. It is also used widely in nuclear power reactors as control rods. Due to having good resistivity it is used in high temperature devices.