Maharashtra Board Class 12 Chemistry Chapter 8 Transition And Inner Transition Elements PDF Download

8. Transition And Inner Transition Elements

Do you know? In which block of the modern periodic table are the transition and inner transition elements placed?

8.1 Introduction

The transition elements belong to d block of the periodic table. As per IUPAC convention the transition metal atom has an incomplete d-subshell or it give cations with incomplete d subshell. They exhibit properties between those of s and p block elements. The transition elements of the modern periodic table appear as groups 3 to 12 or as four long periods. The (n-1) d-orbital is comprised of successively filled in each element, where 'n' is the ultimate or valence shell. The 3d series is comprised of elements from scandium (Z=21) to zinc (Z=30), 4d series has elements from yttrium (Z=39) to cadmium (Z=48), 5d series from lanthanum (Z=57) to mercury (Z=80) without those from cerium to lutecium, and 6d series has actinium to curium without those fromthorium to lawrentium. The general electronic configuration of transition elements is (n-1)d\(^{1-10}\) ns\(^{1-2}\).

8.2 Position In The Periodic Table

The transition elements are placed in the periods 4 to 7 and groups 3 to 12 those constitute 3d, 4d, 5d and 6d series (Fig.8.1).

They are placed at the centre with s block on one side and p on the other. The electropositivity, reactivity and other properties show a gradual change from s block to p block through those of the d block elements.

8.3 Electronic Configuration

The 3d series begins with Sc (Z = 21) and ends with Zn (Z=30). Argon, Ar is the noble gas preceding to 3d series and its electronic configuration is 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\) 3p\(^6\). Calcium (Z = 20) belonging to 's' block of 4th period has electronic configuration 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\) 3p\(^6\) 4s\(^2\). Hence 21st electron in scandium (Z = 21) enters in the available 3d orbital. Electronic configuration of Sc is written as 1s\(^2\) 2s\(^2\) 2p\(^6\) 3s\(^2\) 3p\(^6\) 3d\(^1\) 4s\(^2\) or also can be represented as [Ar] 3d\(^1\) 4s\(^2\).

Teacher's Note

Transition metals are in the middle of the periodic table. In India, iron is used to make many things like tools and machines.

Exam Trick

Remember: Transition = d block. The d electrons fill slowly. Just like students transition from class 6 to class 7, electrons transition into d orbitals.

Points To Remember

Transition elements are in groups 3 to 12 of the periodic table.
They have incomplete d orbitals or can form ions with incomplete d orbitals.
Their general electronic configuration is (n-1)d\(^{1-10}\) ns\(^{1-2}\).
The d orbitals fill between s and p blocks.
They show properties between s and p block elements.

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