Question

Give a reason for the following:

Ti³⁺ salts are coloured whereas Ti⁴⁺ salts are colourless. 

[Given: Atomic number of Ti = 22]

Answer 1

The colour of transition metal salts depends on their electronic configuration and the ability of their d-electrons to undergo d–d transitions when they absorb visible light. Titanium (Ti), with atomic number 22, has the electronic configuration 1s²2s²2p⁶3s²3p⁶3d²4s².

The Ti³⁺ ion (3d¹) contains one unpaired d-electron, which can undergo d-d transitions, causing absorption of visible light and giving colour to its compounds. In contrast, the Ti⁴⁺ ion (3d⁰) has no d-electrons, so d-d transitions are not possible, and hence Ti⁴⁺salts are colourless.