Question

Why ticl3 is coloured while ticl4 is colourless ?

Answer 1

The electronic configuration of Ti is [Ar]3d24s2 . In TiCl3 the oxidation state of Ti is +3 while in TiCl4 the oxidation state of Ti is +4. In case of TiCl3 there is one d electron present in 3d subshell. When light falls on the Ti3+ complex, the t2g electronis excited to eglevel.this excitation take polace in greenish yellow region (≈ 5000 A°), the rest is transmitted. the complementary colour is transmitted which is violet.  The colour due to this transition is called d-d transition. In the absence of ligands, crystal field splitting does not occur, colour disappears.Hence, anhydrous TiCl3  is colourless, but Ti(H2O)6Cl3 is violet. In Ti+4 complex, there is no d electrons, hence d-d transition is not possible. 

Answer 2

Answer:

The magnetic field attracts paramagnetic elements, which are those that contain unpaired electrons in their orbitals. The diamagnetic elements that have paired electrons are weakly attracted to the external magnetic field.

Explanation:

The ground state electronic configuration of titanium is 3d² 4s².

In TiCl₃, titanium is in a +3 oxidation state. So its electronic configuration is 3d¹ 4s⁰. Thus, it has an unpaired electron, which makes the compound paramagnetic in nature. Due to this one unpaired electron transition takes place which makes the compound colored in nature.

In TiCl₄, titanium is in a +4 oxidation state. So its electronic configuration is 3d⁰ 4s⁰. Thus, it has no unpaired electron, which makes the compound diamagnetic in nature. Due to no unpaired electron, no transition takes place which makes the compound colorless in nature.

Due to the titanium's +3 oxidation in TiCl₃, there is one unpaired electron. However, TiCl₄ has a +4 oxidation, which means that there isn't an unpaired electron in the 3d orbital, making it colorless and diamagnetic.

Hence, TiCl₃ is colored while TiCl₄ is colorless due to the absence or presence of an unpaired electron.

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