What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

Why are Zn, Cd and Hg not regarded as transition metals?

They have a fully filled \(d^{10}\) configuration in their ground state and common ions, so the d subshell is complete.

Why do transition metals show variable oxidation states?

The \((n-1)d\) and \(ns\) electrons have similar energies, so a varying number can be lost.

Why are many transition metal ions coloured?

Because of d-d electronic transitions that absorb visible light when the d orbitals are partially filled.

What is the lanthanoid contraction and one of its consequences?

The gradual decrease in size across the lanthanoids; it makes the radii of the second and third transition series nearly equal.

Why do transition metals form complex compounds readily?

They have small, highly charged ions with vacant d orbitals available to accept lone pairs from ligands.

Why do many transition metals and their compounds act as catalysts?

They provide variable oxidation states and surfaces that adsorb reactants, lowering the activation energy.

Why are the atomic radii of transition elements nearly constant across a series?

The increasing nuclear charge is largely offset by the screening effect of added d electrons.

Write the formula and one use of potassium permanganate.

KMnO\(_4\); it is a powerful oxidising agent used in titrations and as a disinfectant.

Why are actinoids all radioactive?

Their nuclei are unstable due to the large number of protons and neutrons in the heavy 5f elements.

How is the spin-only magnetic moment calculated?

By \(\mu=\sqrt{n(n+2)}\) Bohr magnetons, where \(n\) is the number of unpaired electrons.

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

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Transition metals are defined as elements with:

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