The d & f Block Elements Chapter 8 Class 12 Chemistry NCERT Textbook PDF

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Chapter 8: The d & f Block Elements

The d-block of the periodic table contains the elements of the groups 3-12 in which the d orbitals are progressively filled in each of the four long periods.

The elements constituting the f -block are those in which the 4 f and 5 f orbitals are progressively filled in the latter two long periods; these elements are formal members of group 3 from which they have been taken out to form a separate f-block 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 three series of the transition metals, 3d series (Sc to Zn), 4d series (Y to Cd), and 5d series (La to Hg, omitting Ce to Lu).

The fourth 6d series which begins with Ac is still incomplete. The two series of the inner transition metals, (4f and 5f) are known as lanthanoids and actinoids respectively.

Strictly speaking, a transition element is defined as the one which has incompletely filled d orbitals in its ground state or in any one of its oxidation states.

Zinc, cadmium, and mercury of group 12 have full d 10 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 three transition series, their chemistry is studied along with the chemistry of the transition metals.

The presence of partly filled d or f orbitals in their atoms set the study of the transition elements and
The d- and f Block Elements The d- and f Block Elements 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 K2Cr 2O7 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 behavior.

Objectives

Iron, copper, silver, and gold are among the transition elements that have played important roles in the development of human civilization.

The inner transition elements such as Th, Pa, and U are proving excellent sources of nuclear energy in modern times.

their compounds apart from that of the main group elements. However, the usual theory of valence as
applicable to the main group elements can also be applied successfully to the transition elements.

Various precious metals such as silver, gold, and platinum and industrially important metals like iron, copper, and titanium form part of the transition metals.

In this Unit, besides the introduction, we shall first deal with the electronic configuration, occurrence, and general characteristics of the transition elements with special emphasis on the trends in the properties of the first row (3d) transition metals and 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 the chemical reactivity of the inner transition metals.

Author	NCERT
Language	English
No. of Pages	28
PDF Size	1288 KB
Category	Chemistry
Source/Credits	ncert.nic.in

NCERT Solutions Class 12 Chemistry Chapter 8 The d & f Block Elements

Q 8.1:

Write down the electronic configuration of:

(i) Cr³⁺ (ii) Pm³⁺ (iii) Cu⁺ (iv) Ce⁴⁺ (v) Co²⁺ (vi) Lu²⁺ (vii) Mn²⁺  (viii) Th⁴⁺

Ans :

(i) Cr³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³

Or, [Ar]¹⁸ 3d³

(ii) Pm³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f⁴

Or, [Xe]⁵⁴ 4f⁴

(iii) Cu⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰

Or, [Ar]¹⁸ 3d¹⁰

(iv) Ce⁴⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶

Or, [Xe]⁵⁴

(v) Co²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷

Or, [Ar]¹⁸ 3d⁷

(vi) Lu²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹

Or, [Xe]⁵⁴ 4f¹⁴ 5d¹

(vii) Mn²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵

Or, [Ar]¹⁸ 3d⁵

(viii) Th⁴⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶

Or, [Rn]⁸⁶

Q 8.2:

Why are Mn²⁺ compounds more stable than Fe towards oxidation to their +3 state?

Ans : 

Electronic configuration:               Fe²⁺ is [Ar]¹⁸ 3d⁶.

Mn²⁺ is [Ar]¹⁸ 3d⁵.

We know that half and completely filled orbitals are more stable. Hence, Mn with (+2) state has a stable d⁵ configuration, which is why Mn²⁺ shows resistance to oxidation to Mn³⁺.

We know that Fe²⁺ has 3d⁶ configuration and by losing one electron, its configuration changes to a more stable 3d⁵ configuration. Therefore, Fe²⁺ easily gets oxidized to Fe⁺³ oxidation state.

Q 8.4:

To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.

Ans :

The oxidation states with the maximum number (+2 to +7) are exhibited by the elements of Mn oxidation states that are in the first half of the transition series. Ti  With the increase in atomic number, the stability of +2 oxidation state increases.

Once more electrons are filled in the d-orbital, this happens to a great extent.  The +2 oxidation state is not shown by the Sc. Its electronic configuration is 4s² 3d¹.

It loses all the three electrons to form Sc³⁺, +3 oxidation state of Sc is very stable as by losing all three electrons, it attains stable noble gas configuration, [Ar], Ti (+ 4) and V(+5) are very stable for the same reason. For Mn, +2 oxidation state is very stable as after losing two electrons, its d-orbital is exactly half-filled, [Ar] 3d⁵

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