The d- and f-Block Elements

These flashcards cover definitions, periodic trends, electronic configurations, oxidation states, properties, important compounds, and comparisons for the d- and f-block elements as presented in the lecture notes.

Which groups of the periodic table constitute the d-block?

Groups 3–12, in which the (n-1)d orbitals are progressively filled.

What names are given to the elements of the d- and f-blocks?

d-block elements are called transition metals; f-block elements are called inner-transition metals (lanthanoids and actinoids).

According to IUPAC, how is a transition metal defined?

A metal whose atom or at least one common ion has an incompletely filled d subshell.

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

Their atoms and common ions have a completely filled d¹⁰ configuration.

List the four transition-metal series with their orbital designations.

3d (Sc→Zn), 4d (Y→Cd), 5d (La & Hf→Hg), 6d (Ac & Rf→Cn).

Which two series make up the f-block?

The 4f series (Ce→Lu) called lanthanoids, and the 5f series (Th→Lr) called actinoids.

What exceptional ground‐state configurations occur in the 3d series?

Cr: 3d⁵4s¹ and Cu: 3d¹⁰4s¹ due to extra stability of half-filled or filled d subshells.

Why is Pd’s configuration 4d¹⁰5s⁰ instead of the expected 4d⁹5s¹?

Complete filling of 4d gives lower energy, so the 5s electron drops into 4d.

State two typical metallic properties displayed by almost all transition metals.

High tensile strength and high electrical/thermal conductivity (others: ductility, metallic lustre, high melting point).

Why do transition metals have high enthalpies of atomisation?

Many unpaired d electrons contribute to strong metallic bonding by forming extensive metal–metal interactions.

How does the melting point trend across a transition series?

Rises to a maximum around the d⁵ configuration, then falls toward the series end.

Explain the general decrease in ionic radius across a transition series.

Increasing nuclear charge with ineffective d-electron shielding contracts the size of M²⁺ or M³⁺ ions.

What is lanthanoid contraction?

The steady decrease in atomic/ionic radii from La³⁺ to Lu³⁺ due to poor shielding by 4f electrons.

Give one consequence of the lanthanoid contraction.

3rd-row transition elements (e.g., Hf) have radii similar to their 2nd-row analogues (e.g., Zr), making their separation difficult.

Why is the 3d ionisation-enthalpy trend relatively flat compared with p-block elements?

Electrons are removed from nearly degenerate 4s and 3d orbitals whose energies change gradually with atomic number.

Which 3d element exhibits the widest range of oxidation states and why?

Manganese; it can access all states from +2 to +7 because its half-filled d⁵ configuration can lose or share varying numbers of electrons.

Why does the +2 oxidation state become increasingly stable from Sc to Zn?

Rising second ionisation enthalpy and increasing lattice/hydration energies favour the M²⁺ state toward series end.

Explain why Cu has a positive E°(Cu²⁺/Cu) value (+0.34 V).

High enthalpy of atomisation and relatively low hydration enthalpy do not compensate for the large energy needed to remove the second electron from Cu.

Why is Cr²⁺ a strong reducing agent whereas Mn³⁺ is a strong oxidising agent?

Cr²⁺ (d⁴) tends to reach the more stable d³ (t₂g³) state; Mn³⁺ (d⁴) tends to be reduced to the very stable d⁵ configuration.

Write the ‘spin-only’ formula for magnetic moment and state its units.

μ = √[n(n+2)] Bohr magnetons (BM), where n = number of unpaired electrons.

What causes colour in aqueous transition-metal ions?

d–d electronic transitions that absorb visible light; the observed colour is the complementary colour of light absorbed.

Give the observed colour of aqueous MnO₄⁻ and the reason for its intensity.

Deep purple; charge-transfer transitions between Mn and O produce strong absorption.

Why do transition metals readily form complex compounds?

They have small, highly charged ions and vacant d orbitals that accept lone pairs from ligands, leading to coordinate bonding.

Define interstitial compounds and cite one example.

Non-stoichiometric compounds where small atoms (H, C, N) occupy interstitial holes in a metal lattice, e.g., TiC.

State two characteristics of interstitial compounds.

Very hard with high melting points and they retain metallic conductivity.

What industrial catalyst uses V₂O₅ and for which process?

V₂O₅ catalyses SO₂ oxidation in the Contact Process for manufacturing H₂SO₄.

Outline the first step in preparing potassium dichromate from chromite ore.

Fuse FeCr₂O₄ with Na₂CO₃ in air to form Na₂CrO₄, separating iron as Fe₂O₃.

Why does acidified K₂Cr₂O₇ oxidise Fe²⁺ to Fe³⁺?

Dichromate has a high positive reduction potential (Cr₂O₇²⁻/Cr³⁺, E° ≈ +1.33 V) enabling it to accept electrons from Fe²⁺.

Give the disproportionation reaction of MnO₄²⁻ in acidic medium.

3 MnO₄²⁻ + 4 H⁺ → 2 MnO₄⁻ + MnO₂ + 2 H₂O.

Which oxidation states of lanthanoids are most common?

+3 is predominant; +2 and +4 occur occasionally when f⁰, f⁷ or f¹⁴ stability is possible.

What is mischmetall and one of its uses?

An alloy (~95 % lanthanoid metals, 5 % Fe) used in Mg-based alloys and lighter flints.

Why is Ce⁴⁺ a powerful oxidising agent?

Although Ce⁴⁺ attains the noble-gas 4f⁰ configuration, its high E° (+1.74 V) drives reduction back to the more stable +3 state.

Define actinoid contraction.

Progressive decrease in atomic/ionic radii from Th to Lr due to poor shielding by 5f electrons.

State the highest oxidation state reached within the actinoid series and in which element.

+7 in neptunium (Np) and plutonium compounds such as NpO₅ and PuO₆⁻.

How do actinoids differ from lanthanoids in oxidation behaviour?

Actinoids exhibit a wider range of oxidation states (+3 to +7) because 5f, 6d and 7s orbitals have comparable energies, whereas lanthanoids are mostly +3.

Why are later actinoid studies experimentally difficult?

Elements beyond uranium are highly radioactive with very short half-lives (minutes to days) and available only in micro- or nanogram amounts.

What causes the complex magnetic behaviour of actinoids compared with lanthanoids?

5f electrons are less shielded and participate more in bonding, giving varied spin–orbit coupling and magnetic moments.

List two everyday applications that rely on transition-metal compounds.

(1) Fe catalyst in the Haber process for NH₃ production; (2) AgBr light-sensitivity in photographic film.

Why are the highest oxidation states of transition metals generally found in oxides or fluorides?

Small, highly electronegative O and F atoms stabilise high positive charges through strong M–O or M–F bonds (high lattice or bond enthalpy).

Which first-row transition metal most frequently forms the +1 oxidation state and why?

Copper, because the Cu⁺ ion has the stable 3d¹⁰ configuration.