The d- and f-Block Elements
Class 12 Chemistry · Chemistry Part I · Chapter 4
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Summary
The d-block consists of groups 3 to 12, in which the d orbitals are progressively filled across four long periods; these are the transition metals. The f-block, the inner transition metals, comprises the lanthanoids (filling 4f) and actinoids (filling 5f), placed separately at the foot of the periodic table. A transition metal is one with an incomplete d subshell in the atom or its common ions, so zinc, cadmium and mercury are excluded. Transition elements show characteristic properties: high melting points and densities from strong metallic bonding involving d electrons, variable oxidation states because \((n-1)d\) and \(ns\) electrons have similar energies, formation of coloured ions due to d-d electronic transitions, strong tendency to form complex ions, paramagnetism from unpaired d electrons, and catalytic activity. Their atomic radii are nearly constant across a series. The lanthanoids are remarkably similar to one another, and the steady decrease in size across the series, the lanthanoid contraction, makes the second and third transition series alike in size. Actinoids show a wider range of oxidation states and are all radioactive. Important compounds include potassium dichromate and potassium permanganate, strong oxidising agents prepared from their ores.
Position and general electronic configurationPhysical properties and oxidation statesColour, magnetism and catalytic behaviourComplex formation and interstitial compoundsLanthanoids and lanthanoid contractionActinoids and important compounds (K2Cr2O7, KMnO4)
Key terms
Transition element
An element with an incomplete d subshell in its atom or in one of its common ions.
Variable oxidation state
The existence of several stable oxidation states because \((n-1)d\) and \(ns\) electrons have comparable energies.
Lanthanoid contraction
The steady decrease in atomic and ionic radii across the lanthanoid series due to poor shielding by 4f electrons.
Paramagnetism
Attraction into a magnetic field arising from unpaired electrons; measured by the spin-only magnetic moment.
Interstitial compound
A compound formed when small atoms like H, C or N occupy holes in the metal lattice.
Inner transition metal
An f-block element (lanthanoid or actinoid) in which 4f or 5f orbitals are filled.
Extra questions & answers
Try one from this chapter
Transition metals are defined as elements with: