Ch 4Transition and Inner Transition Elements — Class 12 Chemistry, concept-first.

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

The transition metals occupy groups 3 to 12 of the modern periodic table, forming three complete horizontal series plus a partial, radioactive seventh-period series.

Building on the Aufbau principle and Hund's rule learnt in Class XI, the electronic configurations of the d-block elements follow a clear rule with two well-known exceptions.

Having established how the general electronic configuration Noble gasd¹⁻¹⁰ns¹⁻² arises, this section works through ten distinct physical and chemical consequences of that configuration across the 3d t…

All the transition elements are metals -- there are no non-metallic or metalloid d-block elements. Like metals generally, they are good conductors of both heat and electricity; of all known elements,…

The generally expected pattern across any period of the periodic table is a steady decrease in atomic radius as one moves left to right, driven by the rising nuclear charge pulling the (constant-shell…

Ionization enthalpy across the transition series is intermediate in magnitude between the low ionization enthalpies typical of s-block metals (which lose an electron readily) and the higher ionization…

The very first element of the 3d transition series, scandium, is atypical among transition metals in exhibiting only a single oxidation state, +3.

Redox reactions always involve the transfer of electrons from one reacting species to another, and the two halves of any redox reaction are inescapably coupled: whenever one substance is oxidised (los…

Most compounds of the transition elements are paramagnetic, and this magnetic behaviour is directly tied to the electronic configuration of the atom or ion in question.

Chemical industries manufacture an enormous range of everyday and specialty products -- polymers, flavouring compounds, pharmaceutical drugs and many others -- but a large fraction of conventional man…

An alloy is formed by intimately blending a base metal with one or more additional elements, which may themselves be metals, non-metals, or a mixture of both.

An interstitial compound (sometimes also called an interstitial alloy) is a compound formed when small atoms -- typically hydrogen, boron, carbon or nitrogen, all considerably smaller than a typical m…

Transition elements show a marked tendency to form coordination compounds (complexes) with any species -- termed a ligand -- that possesses the ability to donate a lone pair of electrons, forming a co…

Having covered the general trends of the 3d transition series in section 4.3, this section turns to specific, named compounds of transition elements, beginning with a general survey of transition-meta…

The systematic survey of oxidation state versus acid-base character introduced in section 4.4 is developed here in more explicit detail, using chromium's own oxide series as the clearest worked illust…

Potassium dichromate, K₂Cr₂O₇, is one of the two chapter-defining named compounds of transition-metal chemistry studied here in full depth (the other being potassium permanganate, section 4.4.3).

The industrial preparation of potassium dichromate begins with chromite ore (chemically, FeCr₂O₄, essentially iron(II) chromite), which is first concentrated by gravity separation to remove lighter, u…

Potassium dichromate is characteristically an orange-red crystalline solid, melting at 671 K. Its aqueous solubility behaviour is strongly temperature dependent: the compound is only moderately solubl…

Both the chromate ion (CrO₄²⁻) and the dichromate ion (Cr₂O₇²⁻) are oxoanions of chromium, and both act as moderately strong oxidising agents; in both ions, without exception, the chromium is present…

Potassium dichromate acts as a powerful oxidising agent specifically in ACIDIC medium (its oxidising power in neutral or alkaline medium is comparatively much weaker, in contrast with potassium perman…

Potassium dichromate finds a range of important practical applications across industry and analytical chemistry, four of which are highlighted in the chapter.

Potassium permanganate, KMnO₄, is the chapter's second flagship named transition-metal compound, standing alongside potassium dichromate as one of the two most industrially and analytically important…

The industrial preparation of potassium permanganate proceeds from pyrolusite ore (chemically manganese dioxide, MnO₂) in two clearly separated stages.

Potassium permanganate occurs as dark purple crystals, melting at 513 K -- a somewhat lower melting point than that of potassium dichromate (671 K), consistent with the more covalent, less purely ioni…

The permanganate ion, MnO₄⁻, adopts a regular TETRAHEDRAL geometry, directly analogous to the tetrahedral geometry already established for the chromate ion (section 4.4.2.3).

Potassium permanganate is a strong oxidising agent whose specific oxidising behaviour differs markedly depending on the reaction medium in which it is used -- neutral, alkaline (basic), or acidic -- w…

Potassium permanganate finds a wide range of important practical applications, five of which are highlighted in the chapter.

The second half of this unit turns from the d-block elements studied so far to the f-block, or inner transition, elements -- so called because the differentiating electron that distinguishes each succ…

Although the true, formal position of the lanthanoid elements within the periodic table, based strictly on electron-filling order, is group number 3 and period number 6 (directly below lanthanum's own…

Building on the general Aufbau-based approach already used for the d-block (section 4.2), the electron-filling order for the lanthanoid series is worked through element by element, starting from the A…

The single most common, dominant oxidation state shown by every one of the fourteen lanthanoids, without exception, is +3 -- this universal +3 tendency is, as already noted in section 4.5.1, one of th…

As one moves progressively across the 4f series from cerium to lutetium, both the atomic radius and, more particularly, the ionic radius of the Ln³⁺ ions show a gradual, cumulative decrease with incre…

The fourteen elements immediately following actinium -- running from thorium (Th, atomic number 90) through to lawrencium (Lr, atomic number 103) -- are collectively termed the actinoids, directly ana…

Unlike the lanthanoid series, where the electron-filling pattern across the 4f sub-shell is, with only the two well-documented exceptions at gadolinium and lutetium, fairly clean and predictable, the…

Like the lanthanoids, the single most common oxidation state shown across the actinoid series is +3. However, the actinoid series as a whole shows FAR greater variability in accessible oxidation state…

Having developed the electronic configuration and oxidation-state chemistry of the lanthanoid series (sections 4.5.2-4.5.4) and the actinoid series (section 4.5.5) separately, this section draws the t…

This chapter has developed the chemistry of the transition and inner transition elements across two connected halves.

The chapter-end evaluation tests the full span of material developed across both halves of the unit. Part I (Choose the Best Answer, 19 MCQs) probes: why Sc is a transition element but Zn is not; whic…

Sample papers and previous-year board questions for this subject.