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The d-And-f-Block Elements
Question
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Predict which of the following will be coloured in aqueous solution? Ti3+, V3+, Cu+, Sc3+, Mn2+, Fe3+ and Co2+. Give reason for each.

Answer

A transition metal ion in coloured if it has one or more unpaired electron in (n-\)d orbitals i.e. 3d orbitals in case of first transition series. When such species are exposed to visible radiation, d-d transition can take place.

In order to predict colour, let us examine (n – 1)d configuration of each specie.

Ti3+

3d1 configuration

Species is coloured (purple)

V3+

3d2 configuration

Species is coloured (green)

Cu+

3d10 4s°configuration

Species is colourless.

Sc3+

3d° 4s0

It does not contain unpaired e– in 3d orbitals.

Mn2+

3d5

Colourles. It does not contain unpaired electron in 3d-orbitals coloured (pink). All 5 electrons unpaired in five 3d orbitals.

Fe3+

3d5

Coloured (yellow). All 5 electrons unpaired in 3d orbitals.

Co2+

 

3d7

 

Coloured (pink). Three e– unpaired in 3d-orbitals.

 

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Some More Questions From The d-And-f-Block Elements Chapter

Which is a stronger reducing agent Cr2+ or Fe2+ and why?

Explain why Cu+ ion is not stable in aqueous solutions?

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

The outer electronic configuration of copper is 3d10 4s1, yet it is considered transition element. Why?

Why the melting points of transition elements are high?

Why Zn, Cd and Hg are not regarded as transition elements?

Name the first element of 3rd transition series.

Though copper, silver and gold have completely filled sets of d-orbitals yet they are considered as transition metals. Why?