Describe the occurrence (with one named ore each for chromium, manganese and iron) and the general physical ch

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Q. Describe the occurrence (with one named ore each for chromium, manganese and iron) and the general physical characteristics of the first-row transition metals.

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Concept understanding — Position and Electronic Configuration of Transition Elements

By the IUPAC definition, a transition metal is an element whose atom has an incomplete d sub-shell, or which can give rise to a cation with an incomplete d sub-shell. Transition metals occupy the central block of the periodic table (groups 3-12), forming a bridge between the highly reactive s-block metals and the mostly non-metallic p-block elements -- their properties are genuinely transitional between the two. Except for the group-11 metals (Cu, Ag, Au), transition metals are hard solids with very high melting points, and they are good conductors of heat and electricity.

There are three complete transition series: the 3d series (Sc to Zn, period 4, 10 elements), the 4d series (Y to Cd, period 5, 10 elements), and the 5d series (La, then Hf to Hg, period 6, 10 elements) -- plus a partial, entirely radioactive 7th-period series (Ac, Rf to Cn) whose members (bar actinium) are all synthetic with very short half-lives. Zn, Cd and Hg (group 12) have a completely filled d¹⁰ configuration in both their elemental and normal +2 states, so strictly they fail the IUPAC test -- but they are conventionally still classed as transition metals because their properties are a direct extension of their transition-metal neighbours.

Following the Aufbau principle, 4s fills before 3d, so 3d filling genuinely begins only at scandium, [Ar]3d¹4s², and completes at zinc, [Ar]3d¹⁰4s². Chromium and copper are the two well-known exceptions: Cr is [Ar]3d⁵4s¹ (not the 'expected' 3d⁴4s²) and Cu is [Ar]3d¹⁰4s¹ (not 3d⁹4s²) -- in both, one 4s electron shifts into 3d to reach the extra-stable half-filled (d⁵) or fully-filled (d¹⁰) configuration, a stability rooted in the symmetrical, exchange-energy-favoured distribution of electrons across the five d orbitals. Accounting for these exceptions, the general configuration of the d-block is Noble gasd¹⁻¹⁰ns¹⁻², n = 4 to 7; in periods 6 and 7 (except La/Ac) this extends to include a filled (n-2)f¹⁴ term, foreshadowing the f-block.

Transition metals occur in the earth's crust chiefly as oxide, sulfide and mixed-oxide ores, rather than in the free (native) state, since most of them are reactive enough to combine with atmospheric oxygen and other elements over geological time.

Chromium occurs almost entirely as chromite, $\text{FeCr}_2\text{O}_4$ , an iron-chromium spinel oxide; this is the sole industrial starting material for the manufacture of potassium dichromate, covered in detail later in this chapter. Manganese occurs chiefly as pyrolusite, $\text{MnO}_2$ , the starting material for the manufacture of potassium permanganate. Iron, the most abundant transition metal, occurs very widely as haematite, $\text{Fe}_2\text{O}_3$ , and magnetite, $\text{Fe}_3\text{O}_4$ .

General physical characteristics. Transition metals are, with only a few exceptions (notably the distinctive colours of copper and gold), hard, lustrous, silvery-white or grey solids at room temperature. They have comparatively high melting and boiling points and high enthalpies of atomization, because the inner d electrons -- in addition to the outer s electrons -- participate in the delocalized metallic bonding that holds the solid metal lattice together; the more unpaired d electrons available for this bonding, the stronger the metallic bond tends to be. They are excellent conductors of heat and electricity, are mechanically strong, and -- because their atoms across a given period are all of fairly comparable size (the radius varying only modestly across the series, as developed in a later section) -- they readily form alloys with one another and with other metals: steel (iron with chromium, manganese, nickel and others), brass (copper and zinc) and bronze (copper and tin) are everyday examples of this alloy-forming tendency.

✓Final answer

\text{FeCr}_2\text{O}_4

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2025Set ANNUAL1 markMCQ
$Q. In Ni(CO)4 electronic configuration and oxidation state of Ni is$
(a) [Ar]3d⁸ 4s², 0
(b) [Ar]3d⁸, +2
(c) [Ar]3d¹⁰, 0
(d) [Ar]3d⁸ 4s², +2
›Reveal solutionSolution

$Ni(CO)_4$ is a zero-oxidation-state complex; Ni's $4s^2$ electrons rearrange into the 3d subshell, giving $[Ar]3d^{10}4s^0$ .

CO is a neutral ligand (it donates a lone pair from carbon but carries no charge), so it does not oxidise the metal. Since all four ligands in $Ni(CO)_4$ are neutral CO molecules and the overall complex is neutral, the oxidation state of Ni must be 0.

A free, ground-state Ni atom has the configuration $[Ar]3d^8 4s^2$ . In the zero-oxidation-state complex, the 4s electrons are promoted/rearranged into the 3d subshell to give a fully-filled, more symmetric $3d^{10}4s^0$ configuration, which then undergoes $sp^3$ hybridisation (using the empty 4s and three 4p orbitals) to bond tetrahedrally with the four CO ligands.

✓Final answer
$[Ar]3d^{10}$
CBSE 2018Set ANNUAL1 markMCQ
$Q. Which of the following ion will give colourless aqueous solution ?$
(a) $Ni^{2+}$
(b) $Sc^{3+}$
(c) $Cu^{2+}$
(d) $Mn^{3+}$
›Reveal solutionSolution

Colour in transition-metal ions arises from d-d electronic transitions, which require partially-filled d-orbitals ( $d^1$ to $d^9$ ). An ion with $d^0$ (or $d^{10}$ ) configuration cannot undergo a d-d transition and is therefore colourless.

Scandium ( $Z=21$ ) has configuration $[Ar]3d^1 4s^2$ ; losing 3 electrons to form $Sc^{3+}$ removes both $4s$ electrons and the single $3d$ electron, leaving $[Ar]3d^0$ — no d-electrons at all, so $Sc^{3+}$ is colourless (this is why it is sometimes excluded from the 'true' transition series). $Ni^{2+}$ is $3d^8$ (green), $Cu^{2+}$ is $3d^9$ (blue), and $Mn^{3+}$ is $3d^4$ (violet/red) — all have partially-filled d-shells and show characteristic colours from d-d transitions.

✓Final answer
$Sc^{3+}$

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Q.Describe the occurrence (with one named ore each for chromium, manganese and iron) and the general physical characteristics of the first-row transition metals.

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