NCERT Class 12 Books Chemistry Unit 8- The d- and f- Block Elements

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The Chapter Goes Like This-

Objectives

After studying this Unit, you will be able to-

• Learn the positions of the d– and f-block elements in the periodic table
• Know the electronic configurations of the transition (d-block) and the inner transition (f-block) elements
• Appreciate the relative stability of various oxidation states in terms of electrode potential values
• Describe the preparation, properties, structures and uses of some important compounds such as K2Cr2O7 and KMnO4
• Understand the general characteristics of the d– and f–block elements and the general horizontal and group trends in them
• Describe the properties of the f-block elements and give a comparative account of the lanthanoids and actinoids with respect to their electronic configurations, oxidation states and chemical behaviour. 

The d-block of the periodic table contains the elementsof the groups 3-12 in which the d orbitals are progressively filled in each of the four long periods. The f-block consists of elements in which 4 f and 5 f orbitals are progressively filled. They are placed in a separate panel at the bottom of the periodic table. The names transition metals and inner transition metals are often used to refer to the elements of d-and f-blocks respectively.

There are mainly four series of the transition metals, 3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La and Hf to Hg) and 6d series which has Ac and elements from Rf to Cn. The two series of the inner transition metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as lanthanoids and actinoids respectively. 

Originally the name transition metals was derived from the fact that their chemical properties were transitional between those of s and p-block elements. Now according to IUPAC, transition metals are defined as metals which have incomplete d subshell either in neutral atom or in their ions. Zinc, cadmium and mercury of group 12 have full d10 configuration in their ground state as well as in their common oxidation states and hence, are not regarded as transition metals. However, being the end members of the 3d, 4d and 5dm transition series, respectively, their chemistry is studied along with the chemistry of the transition metals. 

The presence of partly filled d or f orbitals in their atoms makes transition elements different from that of the non-transition elements. Hence, transition elements
and their compounds are studied separately. However, the usual theory of valence as applicable to the nontransition elements can be applied successfully to the transition elements also. Various precious metals such as silver, gold and platinum and industrially important metals like iron, copper and titanium belong to the transition metals series. 

In this Unit, we shall first deal with the electronic configuration, occurrence and general characteristics of transition elements with special emphasis on the trends in the properties of the first row (3d) transition metals along with the preparation and properties of some important compounds. This will be followed by consideration of certain general aspects such as electronic configurations, oxidation states and chemical reactivity of the inner transition metals. 

THE TRANSITION ELEMENTS (d-BLOCK)

Position in the Periodic Table 

The d–block occupies the large middle section of the periodic table flanked between s– and p– blocks in the periodic table. The d–orbitals of the penultimate energy level of atoms receive electrons giving rise to four rows of the transition metals, i.e., 3d, 4d, 5d and 6d. All these series of transition elements are shown in Table 8.1. 

Electronic Configurations of the d-Block Elements 

In general the electronic configuration of outer orbitals of these elements is (n-1)d1–10ns1–2. The (n–1) stands for the inner d orbitals which may have one to ten electrons and the outermost ns orbital may have one or two electrons. However, this generalisation has several exceptions because of very little energy difference between (n-1)d and ns orbitals. Furthermore, half and completely filled sets of orbitals are relatively more stable. A consequence of this factor is reflected in the electronic configurations of Cr and Cu in the 3d series. For example, consider the case of Cr, which has 3d5 4s1 configuration instead of 3d44s2; the energy gap between the two sets (3d and 4s) of orbitals is small enough to prevent electron entering the 3d orbitals. Similarly in case of Cu, the configuration is 3d104s1 and not 3d94s2. The ground state electronic configurations of the outer orbitals of transition elements are given in Table 8.1. 
The electronic configurations of outer orbitals of Zn, Cd, Hg and Cn are represented by the general formula (n-1)d10ns2. The orbitals in these elements are completely filled in the ground state as well as in their common oxidation states. Therefore, they are not regarded as transition elements. 

The d orbitals of the transition elements protrude to the periphery of an atom more than the other orbitals (i.e., s and p), hence, they are more influenced by the surroundings as well as affect the atoms or molecules surrounding them. In some respects, ions of a given dn configuration (n = 1 – 9) have similar magnetic and electronic properties. With partly filled d orbitals these elements exhibit certain characteristic properties such as display of a variety of oxidation states, formation of coloured ions and entering into complex formation with a variety of ligands. 

The transition metals and their compounds also exhibit catalytic property and paramagnetic behaviour. All these characteristics have been discussed in detail later in this Unit.

There are greater similarities in the properties of the transition elements of a horizontal row in contrast to the non-transition elements. However, some group similarities also exist. We shall first study the general characteristics and their trends in the horizontal rows (particularly 3d row) and then consider some group similarities. 

You can download the complete book from the link given below. 

NCERT Class 12 Books Chemistry Unit 8- The d- and f- Block Elements- PDF Download

Unit 8: The d- and f- Block Elements

अध्याय 8: d- एवं f- ब्लॉक के तत्व Safalta provides the latest NCERT course books for all the major subjects of Class 12. A team of proficient teachers drafts these matters in a precise and thorough manner. You can download the PDFs for all the subjects in a chapter-wise format.

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