Block D and F Elements

8.47 The given statement is true as explained below:

1. Atomic radii of the heavier transition elements (4d and 5d series) are larger than those of the corresponding elements of the first transition series through those of 4d and 5d series are very close to each (Lanthanoid contraction)

2. Due to stronger intermetallic bonding (M-M bonding), the melting and boiling points of heavier transition elements are greater than those of the first transition series

3. The ionization enthalpies of 5d series are higher than the corresponding elements of 3d and 4d

4. The heavier transition elements form low spin complexes whereas the elements of the first series form low spin or high spin complexes depending upon the strength of ligand field.

The strength of a ligand can be found out relating to its If a species is highly electronegative it has less tendency to donate e-s and thus is a weak field ligand and vice versa

5. +2 and +3 oxidation states are more common for elements in the first transition series, while higher oxidation states are more common for the heavier elements.

8.47 The given statement is true as explained below:

1. Atomic radii of the heavier transition elements (4d and 5d series) are larger than those of the corresponding elements of the first transition series through those of 4d and 5d series are very close to each (Lanthanoid contraction)

2. Due to stronger intermetallic bonding (M-M bonding), the melting and boiling points of heavier transition elements are greater than those of the first transition series

3. The ionization enthalpies of 5d series are higher than the corresponding elements of 3d and 4d

4. The heavier transition elements form low spin complexes whereas the elements of the first series form low spin or high spin complexes depending upon the strength of ligand field.

The strength of a ligand can be found out relating to its If a species is highly electronegative it has less tendency to donate e-s and thus is a weak field ligand and vice versa

5. +2 and +3 oxidation states are more common for elements in the first transition series, while higher oxidation states are more common for the heavier elements.

8.45  (i) Electronic configuration:

In the first transition series, 3d orbitals are progressively filled while in the second and third transition series, 4d and 5d orbitals are filled. However the first series shows only two exceptions Cr and Cu, both have a single electron in the 4s orbital ( 3d⁵ 4s¹, 3d¹⁰ 4s¹) but the second series shows more exceptions. Similarly, third series elements show exceptions. Thus in the same vertical column, in a number of series, the electronic configuration of the three series are not similar at all.

(ii) Oxidation states:

The number of oxidation states shown by the elements in the middle of each series is maximum and minimum at the extreme ends. However, the first row elements differ from the second and third-row elements in the fact that for all the first row elements, +2 and +3 states are important. For second and third row elements, higher oxidation states are more important than those of the first row elements.

(iii) Ionisation enthalpies:

The first ionization enthalpies in each series generally increase gradually as we move from left to right through some exceptions are observed in each series. The first ionization enthalpies of some elements in the second (4d) series are higher while some of them have a lower value than the elements of 3d series in the same vertical column.

However the first ionization enthalpies of third (5d) series are higher than those of 3d and 4d series. This is because of weak shielding of nucleus by 4f electrons in the 5d series

(iv) Atomic sizes:

In general, ions of the same charge or atoms in a given series show progressively decrease in radius with increasing atomic number though the decrease is quite small. But the size of the atoms of the 4d series is larger than the corresponding elements of the 3d series whereas those of corresponding elements of the 5d series are nearly the same as those of4d series because of Lanthanoid contraction

Note: Lanthanoid contraction is the regular decrease (contraction) in the atomic and ionic radii of lanthanoids with increasing atomic number

8.42 The members of lanthanide series along with their electronic configuration are given in the below table:

The typical oxidation state of the lanthanides is +3. The oxidation state of +2 and +4 are exhibited by some of the elements. These are shown by those elements which by losing 2 or 4 elements acquire a stable configuration.

+2 oxidation state is exhibited when the lanthanide has the configuration 5d⁰6s² so that 2 electrons are lost easily. Hence the members which will show +2 oxidation state are:

+2 = ₆₀Nd, ₆₂Sm, ₆₃Eu, ₆₉Tm, ₇₀Yb

+4 oxidation state is exhibited when the configuration left (by losing 2 electrons) is close to 4f⁰ (example 4f⁰ , 4f¹, 4f², 4f³) or close to 4f⁷ (example 4f⁷or 4f⁸) or close to 4f¹⁴ ( 4f¹³ or 4f¹⁴)

Hence, the members which will show +4 oxidation state are:

+4 = ₅₈Ce, ₅₉Pr, ₆₀Nd, ₆₅Tb, ₆₆Dy

Each case tends to revert to the more stable oxidation state of +3 by loss or gain of an That is why Sm²⁺, Eu²⁺ and Yb²⁺ ions in solutions are good reducing agents and aqueous solution of Ce⁴⁺ and Tb⁴⁺ are good oxidizing agents.