Transition (d-Block) Elements — Part 1: Position, configuration and periodic trends: visual lesson, ISC Class 12 Chemistry

Lesson

The transition elements

Part 1 — where the d-block sits, how its electrons are arranged, and how size and ionisation enthalpy change across a series.

In this lesson you will

Locate the d-block in the periodic table, define a transition element and name important ores of 3d metals
Write electronic configurations of 3d elements and their ions, including chromium and copper, and note anomalies in the 4d and 5d series
Explain the trends in metallic character, atomic and ionic radii and ionisation enthalpy across the 3d series

Schematic: element symbols are left out so that the blocks stand out.

Concept

Position and definition

The d-block occupies groups 3–12 in periods 4–7: the 3d (Sc–Zn), 4d (Y–Cd), 5d (La, Hf–Hg) and 6d (Ac, Rf–Cn) series. A transition element has an incompletely filled d subshell in its ground state or in one of its common oxidation states. Zn, Cd and Hg (d¹⁰ in atom and common ions) are d-block elements but not typical transition elements.

Table of the four d-series
Series	Period	Elements	Subshell filled
3d	4	Sc to Zn	3d
4d	5	Y to Cd	4d
5d	6	La, Hf to Hg	5d
6d	7	Ac, Rf to Cn	6d

Concept

Occurrence of the 3d metals

Most 3d metals occur combined in ores — oxides, sulfides and carbonates. Iron, titanium and manganese are abundant; copper and gold also occur native (free).

Table of ores of 3d metals with their formulae
Metal	Important ore	Formula
Iron	Haematite, magnetite	Fe₂O₃, Fe₃O₄
Titanium	Ilmenite, rutile	FeTiO₃, TiO₂
Chromium	Chromite	FeCr₂O₄
Manganese	Pyrolusite	MnO₂
Copper	Copper pyrites	CuFeS₂
Zinc	Zinc blende	ZnS
Nickel	Pentlandite	(Ni,Fe)₉S₈

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