F Block Elements - Properties, Oxidation States and Examples

F-block elements are called inner transition elements as they provide a transition in the 6th and 7th rows of the periodic table. They generally have high melting and boiling points. They consist of two series: Lanthanides and actinides. In the periodic table, the element in which the last electrons enter in (n - 2)f orbitals are called f- block elements. They come in the third period of the periodic table with two series 4f and 5f. The 4f series elements are called Lanthanides and the 5f series elements are actinides.

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This Story also Contains

1. Properties of F-Block Elements
2. Some Solved Examples
3. Conclusion

The f-block elements on the periodic table are shown green in the periodic table and contain elements 57-71 called lanthanides, and elements 89-103 being called actinides. Then can be seen in two different chemical series, such as lanthanides under the 4f, and actinides under the 5f block and deep-seated 4f with an increase in atomic number and how the electronic configuration of the f-block element was done. The 5f elements of the actinides constitute the second inner transition metal series, and the lanthanides constitute the first inner transition series in chemistry.

Properties of F-Block Elements

Electronic Configurations

It may be noted that atoms of these elements have an electronic configuration with 6s² common but with variable occupancy of 4f level. However, the electronic configurations of all the tripositive ions (the most stable oxidation state of all the lanthanoids) are of the form 4fⁿ (n = 1 to 14 with increasing atomic number).

Atomic and Ionic Sizes

The overall decrease in atomic and ionic radii from lanthanum to lutetium (the lanthanoid contraction) is a unique feature in the chemistry of lanthanoids. It has far-reaching consequences in the chemistry of the third transition series of the elements. The decrease in atomic radii (derived from the structures of metals) is not quite as regular as it is in M³⁺ ions. This contraction is, of course, similar to that observed in an ordinary transition series and is attributed to the same cause, the imperfect shielding of one electron by another in the same sub-shell. However, the shielding of one 4f electron by another is less than one d electron by another with the increase in nuclear charge along the series. There is a fairly regular decrease in the sizes with increasing atomic number.

Oxidation States

In the lanthanoids, La(II) and Ln(III) compounds are predominant species. However, occasionally +2 and +4 ions in solution or solid compounds are also obtained. This irregularity (as in ionization enthalpies) arises mainly from the extra stability of empty, half-filled, or filled f subshell. Thus, the formation of Ce(IV) is favored by its noble gas configuration, but it is a strong oxidant reverting to the common +3 state. The E^o value for Ce⁴⁺/ Ce³⁺ is + 1.74 V which suggests that it can oxidise water. However, the reaction rate is very slow and hence Ce(IV) is a good analytical reagent. Pr, Nd, Tb, and Dy also exhibit +4 state but only in oxides, MO₂. Eu²⁺ is formed by losing the two s electrons and its f⁷ configuration accounts for the formation of this ion. However, Eu²⁺ is a strong reducing agent changing to the common +3 state. Similarly, Yb²⁺ which has f¹⁴ configuration is a reductant. Tb^IV has half-filled f-orbitals and is an oxidant. The behavior of samarium is very much like europium, exhibiting both +2 and +3 oxidation states.

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Some Solved Examples

Q.1 In the context of the lanthanoids, which of the following statements is not correct?

1)There is a gradual decrease in the radii of the members with increasing atomic number in the series.

2) All the members exhibit a +3 oxidation state

3) Because of similar properties the separation of lanthanoids is not easy.

4) Availability of 4f electrons results in the formation of compounds in the +4 state for all the members of the series.

Solution:

As we learned,

Generally, all Lanthanides form compounds in the +3 oxidation state. Due to Lanthanide contraction, the elements show a gradual decrease in their atomic as well as Ionic radii. These elements are often found together in nature, and as a result of these elements having similar properties, their separation also becomes difficult.

Hence, the answer is the option (4).

Q.2 The outer electronic configuration of Gd (Atomic No: 64) is

1) 4f³5d⁵6s²

2) 4f⁸5d⁰6s²

3) 4f⁴5d⁴6s²

4) 4f⁷5d¹6s²

Solution:

As we learned

The electronic configuration of Gd is given as

Gd⇒1s²,2s²,2p⁶,3s²,3p⁶,4s²,3d¹⁰,4p⁶,5s²,4d¹⁰,5p⁶,6s²,4f⁷,5d¹

It is to be noted that the electronic configuration of Gd accommodates one electron in the 5d orbital as it has a stable, half-filled f⁷ configuration

Hence, the answer is the option (4).

Conclusion

F-block elements play a crucial role in modern science and technology, offering unique properties and applications, albeit with challenges related to their handling and environmental impact. Neodymium, samarium, and others are used to make strong permanent magnets, essential in electronics, wind turbines, and electric vehicles. Lanthanides like europium and terbium are used in color television screens, LED lights, and fluorescent lamps.