Introduction

What this unit sets out to do. By the end of it you should be able to:

• recognise the position of the d-block and f-block elements in the periodic table;
• describe the general trend in properties of the elements of the 3d series;
• discuss the trends in the $M^{n+}/M$ standard electrode potential;
• predict whether a species is oxidising or reducing based on its $E^{0}$ value;
• explain the tendencies of d-block elements to form alloys, complexes and interstitial compounds;
• describe the preparation and properties of potassium permanganate and potassium dichromate;
• describe the properties of the f-block elements, and compare lanthanoids with actinides.

The metallic elements that have an incompletely filled d or f sub-shell, either in the neutral atom or in a cation the atom commonly forms, are called transition metals. By this broad reading, the definition even sweeps in the lanthanoids and actinoids. But the IUPAC definition is narrower and more precise: a transition metal is an element whose atom has an incomplete d sub-shell, OR which can give rise to a cation with an incomplete d sub-shell. These elements sit in the central block of the periodic table, forming a bridge between the highly reactive metals of the s-block on the left and the mostly non-metallic elements of the p-block on the right. Their properties are genuinely transitional between the two: less violently reactive than an alkali or alkaline-earth metal, yet still unmistakably metallic, unlike most p-block elements. With the notable exception of the group-11 elements (Cu, Ag, Au), transition metals are hard solids with very high melting points.

Transition metals have shaped human civilization directly -- iron and copper in particular mark entire ages of technological development -- and they remain industrially indispensable today: tungsten as the filament in incandescent light bulbs (chosen for its extremely high melting point), titanium in artificial joint replacements (biocompatible and strong for its weight), molybdenum as a structural component in boiler plants (heat- and corrosion-resistant), and platinum as a catalyst in countless industrial and automotive processes. They are equally vital to living systems: iron sits at the core of the haemoglobin molecule that carries oxygen in blood, and cobalt is the central metal ion of vitamin B12, essential for nerve function and red blood cell formation.