Question

Explain colour and complex formation tendency of transition metal ions?

Answer 1

Hint: Colour property of transition metal ions can be explained on the basis of $d - d$ transition. If there is $d - d$ transition then only they will show the colour property. The complex formation tendency is shown by those transition ions which have vacant $d - $orbitals.

Complete step by step answer:
First of all we will read about transition elements.
Transition elements: Those elements which are in groups from three to eleven. They are called a transition because they are in between the s- block elements and p-block elements. For example: Scandium, iron, zinc, etc. They have fully or at least one electron in their d-orbits. For example: scandium has one d-electron, zinc has ten d-electrons. Due to the different number of electrons present in their d-shells they show different valencies. For example: Scandium having one electron can show three valencies as one, two and three. Because the atomic number of scandium is $21$ and its electronic configuration is $Ar3{d^1}4{s^2}$. By losing two s-electrons and one d-electron it will achieve three valencies which are stable states of scandium. Because after losing three electrons it will attain electronic configuration of noble gas argon.
$d - d$ transition: The movement of electrons from one d-orbitals to another d-orbitals, is known as $d - d$ transition.
Colouring property in transition elements: Those ions of transition elements will show colouring property which will have unpaired electrons after loss of electrons. For example: Scandium after losing three electrons have no d-electrons so they cannot show $d - d$ transitions. So it will not show colouring property i.e. it will be colourless in nature. Manganese having atomic number $25$ and the electronic configuration of manganese is $Ar3{d^5}4{s^2}$. After losing two electrons it will have five unpaired d-electrons so they can show $d - d$ transitions. So it will show colouring property.
Complex formation by transition ions: Transitions elements or ions show complex formation tendency because they are small in size and they have d-electrons to form new bonds. Due to their small size, d-electrons and high nuclear size they can accept lone pairs of ligands and form complexes.

Note: Ligands: These are the molecules which form bonds with the central metal atom or ions. They can be of two types based on electron pair donor or acceptor. If they accept electron pair i.e. ligand is electron pair acceptor then it is Lewis acid and if it is electron pair donor then they will be Lewis base.