Question

Ti$^2+$ is purple while Ti$^4+$ is colourless because

• A. Ti\(^2+\) has \(3d^2\) configuration
• B. Ti\(^4+\) has \(3d^2\) configuration
• C. Ti\(^2+\) is very small cation when compared to Ti\(^4+\) and hence, doesn't absorb any radiation
• D. There is no crystal field effect in Ti\(^4+\)

Hint:

The presence of unpaired electrons in transition metal ions allows for color due to d-d transitions. Ions with no d-electrons, like Ti\(^4+\), are colorless.

Answer 1

The Correct Option is A

The reason that Ti²⁺ is purple while Ti⁴⁺ is colorless lies in their electronic configurations and the concept of crystal field theory. Let's explore this in detail.

Electronic Configurations:
1. Ti²⁺ has a configuration of [Ar] 3d². This means that in its d-orbital, there are two electrons. Electrons in d-orbitals can absorb visible light, leading to electron transitions, which result in color.

2. Ti⁴⁺ has a configuration of [Ar] with empty 3d orbitals. Since there are no electrons in the d-orbitals, Ti⁴⁺ cannot absorb visible light, thus appearing colorless.

Crystal Field Effect:
The color in transition metal complexes is majorly due to the crystal field splitting of d-orbitals and the transitions of electrons between these split d-orbitals. In Ti²⁺, the presence of 3d electrons allows such transitions, causing the absorption of certain wavelengths of visible light (particularly green and yellow), and the reflection of other wavelengths (such as red and blue), which we perceive as purple. Conversely, for Ti⁴⁺, the absence of d-electrons means no such transitions can occur, thus no color is observable.

Therefore, the correct statement is Ti²⁺ has 3d² configuration.

Answer 2

The color of transition metal ions arises due to the d-d transitions when the d-orbitals split in the presence of a ligand field. In the case of Ti\(^2+\), the electronic configuration is \( [Ar] 3d^2 \), and there are unpaired electrons in the 3d orbitals. 
These unpaired electrons undergo transitions between the split d-orbitals, absorbing specific wavelengths of light, which gives rise to the purple color. On the other hand, Ti\(^4+\) has the electronic configuration \( [Ar] 3d^0 \), which means there are no d-electrons available to undergo these transitions. 
Therefore, Ti\(^4+\) is colorless. 
Thus, the correct answer is Ti\(^2+\) has \(3d^2\) configuration.