Chapter 4 - The d- and f- block elements

The d- and f-Block Elements chapter studies transition metals and inner-transition metals. It connects electronic configuration with variable oxidation states, coloured ions, magnetic behaviour, catalytic activity and complex formation. These elements are important not only in examinations but also in metallurgy, pigments, catalysts, magnets, medicines and biological systems.

Rather than learning every property as an isolated fact, students should repeatedly connect behaviour with partially filled d or f orbitals, effective nuclear charge, atomic size and oxidation state.

Position and electronic configuration

The d-block occupies the middle of the periodic table and contains elements in which the differentiating electron enters a d subshell. A transition element is commonly defined as an element having a partially filled d subshell in its atom or in one of its common oxidation states. This definition explains why not every d-block element is necessarily treated as a transition element.

The general outer electronic configuration is (n−1)d1–10 ns0–2, though important exceptions occur because the energies of the d and s orbitals are close. When ions form, ns electrons are generally removed before (n−1)d electrons.

Trends across the transition series

The chapter examines trends in atomic and ionic radii, ionisation enthalpy, oxidation states, standard electrode potentials, melting points, enthalpy of atomisation and density. These trends are often less regular than those in the s- and p-block because d electrons participate in bonding and shield nuclear charge imperfectly.

Transition metals commonly show variable oxidation states because ns and (n−1)d electrons have similar energies. The highest oxidation states are often found near the middle of a series, while lower oxidation states become more stable toward the end.

Colour, magnetism and complex formation

Many transition-metal ions are coloured because visible light can promote electrons between split d-orbital energy levels. Species with d0 or d10 configurations are often colourless, although charge-transfer effects can create exceptions.

Unpaired electrons produce paramagnetism. The spin-only magnetic moment can be calculated from the number of unpaired electrons. Species with all electrons paired are diamagnetic.

Small size, high charge and available orbitals allow transition-metal ions to accept electron pairs from ligands and form coordination compounds. This tendency is developed further in the next chapter.

Catalytic activity, alloys and interstitial compounds

Transition metals and their compounds are effective catalysts because they can adopt multiple oxidation states and provide surfaces on which reactants are adsorbed. Iron in the Haber process, vanadium(V) oxide in the Contact process and nickel in hydrogenation are standard examples.

Similar atomic sizes allow transition metals to form alloys readily. Small atoms such as hydrogen, carbon or nitrogen can occupy spaces in metal lattices to form interstitial compounds, which are often hard and retain metallic conductivity.

Important compounds: dichromate and permanganate

Potassium dichromate and potassium permanganate are important oxidising agents. Students study their preparation, structures, colour changes and redox reactions in acidic, neutral or alkaline media.

The reduction product depends on the medium. Balancing the relevant half-reaction first is more reliable than memorising complete equations. Colour changes—such as orange dichromate to green chromium(III), or purple permanganate to different manganese products—also appear in qualitative questions.

Lanthanoids

Lanthanoids involve progressive filling of 4f orbitals. The +3 oxidation state is most common, though some elements also show +2 or +4 depending on especially stable electronic arrangements.

Lanthanoid contraction is the gradual decrease in atomic and ionic size across the series caused by poor shielding by 4f electrons. It explains the similarity of later transition pairs, the difficulty of separating lanthanoids and changes in the basic strength of lanthanoid hydroxides.

Actinoids

Actinoids involve filling of 5f orbitals. They are radioactive and show a wider range of oxidation states than lanthanoids because 5f, 6d and 7s orbitals have comparable energies. Their chemistry is complex, and many elements beyond uranium are synthetic.

What can students study on Teachoo?

• electronic configurations of d- and f-block elements;

• the meaning of transition element;

• periodic trends and oxidation states;

• colour and magnetic-moment calculations;

• catalytic behaviour, alloys and interstitial compounds;

• oxidising reactions of dichromate and permanganate;

• lanthanoids and lanthanoid contraction;

• actinoids and their oxidation states; and

• NCERT in-text and exercise solutions.

Common mistakes to avoid

• Do not assume every d-block element is a transition element under the standard definition.

• Remove ns electrons before (n−1)d electrons when forming cations.

• Determine the d-electron count after accounting for oxidation state.

• Do not state that all transition-metal compounds are coloured or paramagnetic.

• Remember that the product of permanganate reduction depends on the reaction medium.

• Distinguish lanthanoid contraction from a general periodic decrease in size.

Best way to study the d- and f-Block Elements

Prepare a trend table across the first transition series, but write a short reason beside each trend. Practise electronic configurations and d-electron counts daily. Learn dichromate and permanganate chemistry through balanced half-reactions and colour observations. Finally, make a comparison sheet for lanthanoids and actinoids.

Frequently asked questions

Are all d-block elements transition elements?

No. A transition element must have a partially filled d subshell in its atom or in a common oxidation state. Elements with consistently complete d subshells may not satisfy this definition.

Why do transition metals show variable oxidation states?

Their ns and (n−1)d orbitals are close in energy, so different numbers of electrons can participate in bonding.

Why are many transition-metal ions coloured?

Light may be absorbed to promote electrons between d orbitals split by the surrounding ligands; the remaining transmitted or reflected light gives the observed colour.

What causes paramagnetism?

One or more unpaired electrons cause attraction to a magnetic field.

Why are transition metals good catalysts?

Their variable oxidation states and ability to adsorb reactants or form intermediates provide lower-energy reaction pathways.

What is lanthanoid contraction?

It is the gradual decrease in the radii of lanthanoid atoms and ions across the series due mainly to poor shielding by 4f electrons.

How are actinoids different from lanthanoids?

Actinoids are all radioactive and generally show a wider range of oxidation states, while lanthanoids most commonly show the +3 state.

Study the d- and f-Block Elements with Teachoo to connect configurations with trends, colours, magnetic behaviour and redox reactions.