Chemistry Class 12 NCERT Solutions: Chapter 8 The d and f Block Elements Part 9

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Q: 36. Write down the number of electrons in each of the following ions:

Indicate how would you expect the five orbitals to be occupied for these hydrated ions (octahedral).

Answer:

Q_36_The Number of 3d Electrons
Q_36_The Number of 3d Electrons

Metal ion

Number of d-electrons

Filling of d-orbital

2

3

3

5

6

5

7

8

9

Q: 37. Comment on the statement that elements of the first transition series possess many properties different from those of heavier transition elements.

Answer:

The properties of the elements of the first transition series differ from those of the heavier transition elements in many ways.

(i) The atomic sizes of the elements of the first transition series are smaller than those of the heavier elements (elements of 2nd and 3rd transition series).

However, the atomic sizes of the elements in the third transition series are virtually the same as those of the corresponding members in the second transition series. This is due to lanthanoid contraction.

(ii) and oxidation states are more common for elements in the first transition series, while higher oxidation states are more common for the heavier elements.

(iii) The enthalpies of atomisation of the elements in the first transition series are lower than those of the corresponding elements in the second and third transition series.

(iv) The melting and boiling points of the first transition series are lower than those of the heavier transition elements. This is because of the occurrence of stronger metallic bonding (M−M bonding).

(v) The elements of the first transition series form low-spin or high-spin complexes depending upon the strength of the ligand field. However, the heavier transition elements form only low-spin complexes, irrespective of the strength of the ligand field.

Q: 38. What can be inferred from the magnetic moment values of the following complex species?

Example Magnetic Moment (BM)

Answer:

Magnetic moment is given as

For value

For value

For value

For value

For value

(i)

For in transition metals, the magnetic moment is calculated from the spin7only formula. Therefore,

We can see from the above calculation that the given value is closest to . Also, in this complex, is in the oxidation state. This means that has electrons in the .

Hence, we can say that is a strong field ligand that causes the pairing of electrons.

(ii)

We can see from the above calculation that the given value is closest to . Also, in this complex, Fe is in the oxidation state. This means that has electrons in the d-orbital.

Hence, we can say that is a weak field ligand and does not cause the pairing of electrons.

(iii)

We can see from the above calculation that the given value is closest to . Also, in this complex, is in the oxidation state. This means that has electrons in the d-orbital.

Hence, we can say that is a weak field ligand and does not cause the pairing of electrons.