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Colour of Ti³⁺ compounds vs zinc compounds

Short answer

Ti3+ (3d1) has a d–d transition, absorbing green-yellow light and appearing violet. Zn2+ (3d10) has a filled d subshell with no vacant orbital for electron excitation, so no visible light is absorbed and compounds are colourless.

Explain why compounds of Ti³⁺ are coloured but those of zinc are colourless.

  • Ti³⁺ is 3d¹: it has one d electron in the t₂g level, which absorbs visible light (about 500 nm) and jumps to the e_g level (d–d transition), so the complementary violet colour is seen.
  • Zinc compounds (Zn²⁺) are 3d¹⁰: the d subshell is completely filled, with no vacant d orbital to which an electron can be excited, so no visible light is absorbed and the compounds are colourless (white).

✓ Answer checked by Claude Opus 5.5 (high effort)

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