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CBSE Class 12th Chemistry Notes: The d- and f-Block Elements (Part-II)

Jagran Josh

This article provides you the revision notes on Class 12 Chemistry: Chapter- The d- and f-Block Elements, to give you a quick glance of the chapter. This article is a continuation of the revision notes on Class 12 Chemistry, Chapter- The d- and f-Block Elements, Part-I. In Part-I you discovered about the d-block elements and their important compounds. In Part-II, you will get acquainted with the f-block elements. These quick notes are prepared strictly according to the latest CBSE syllabus for Class 12th Chemistry.

The main topics covered in this part are:

The key notes of the chapter are as follows:

f –Block elements or Inner Transition elements

The elements in which the differentiating electron enters the penultimate energy level i.e. (n−2)f, are called f-block elements. Due to such electronic configuration where the last electron enters the 4f or 5f orbitals that are lower than the outermost electrons, f-block elements are also named as inner transition elements.

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Depending upon the fact whether the last electron enters the 4f or 5f-orbitals, f-block elements are differentiated into lanthanoids and actinoids.

1. Lanthanoids: The 14 elements immediately following lanthanum, i.e., Cerium (58) to Lutetium (71) are called lanthanoids. They belong to first inner transition series. Lanthanum (57) has similar properties.

General properties of lanthanoids:

Exception: Lu3+ ions do not show any colour due to the absence of any unpaired electron in the 4f subshell which is fully filled.

Exception: Some elements show +2 and +4 oxidation states. This irregularity arises mainly from the extra stability of empty, half-filled or filled f subshell.

For example:


Physical properties of lanthanoids:

Chemical properties of lanthanoids:

Some important chemical reactions of lanthenoids are:


Formation of alloys: Lanthanoids are all used in steel industry for making alloy steels. Important and well-known alloy is misch-metal and it con-sists of lanthanoid (90-95%), iron (4-5%) and trace amount of S, C Ca and Al.


(i) Misch-metal is used in making tracer bullets, shell and lighter flint.

(ii) Mixed oxides of lanthanoids are used as a catalyst in petroleum cracking. Some individual oxides of lanthanoids are used as phosphors in television screens and similar fluorescing surface.

2. Actinoids:  The 14 elements immediately following actinium (89), with atomic numbers 90 (Thorium) to 103 (Lawrencium) are called actinoids. They belong to second inner transition series. In actinoids the filling of electrons takes place in the anti-penultimate  subshell.

General properties of actinoids:

Chemical properties:

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