Its oxidising action is as shown below.
\(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+14 \mathrm{H}^{+}+6 \mathrm{e}^{-} \rightarrow \mathrm{Cr}^{3+}+7 \mathrm{H}_{2} \mathrm{O}\)
(i) It oxidises ferrous salts to ferric salts.
\(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+6 \mathrm{Fe}^{2+}+14 \mathrm{H}^{+} \rightarrow 2 \mathrm{Cr}^{3+}+6 \mathrm{Fe}^{3+}+7 \mathrm{H}_{2} \mathrm{O}\)
(ii) It oxidises iodide ions to iodine.
\(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+6 \mathrm{I}^{-}+14 \mathrm{H}^{+} \rightarrow 2 \mathrm{Cr}^{3+}+3 \mathrm{I}_{2}+7 \mathrm{H}_{2} \mathrm{O}\)
(iii) It oxidises sulphide ion to Sulphur.
\(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+3 \mathrm{~S}^{2-}+14 \mathrm{H}^{+} \rightarrow 2 \mathrm{Cr}^{3+}+3 \mathrm{~S}+7 \mathrm{H}_{2} \mathrm{O}\)
(iv) It oxidises Sulphur dioxide to sulphate ion.
\(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+3 \mathrm{SO}_{2}+2 \mathrm{H}^{+} \rightarrow 2 \mathrm{Cr}^{3+}+3 \mathrm{SO}_{4}^{2-}+\mathrm{H}_{2} \mathrm{O}\)
(v) It oxidises stannous salts to stannic salt.
\(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+3 \mathrm{Sn}^{2+}+14 \mathrm{H}^{+} \rightarrow 2 \mathrm{Cr}^{3+}+3 \mathrm{Sn}^{4+}+7 \mathrm{H}_{2} \mathrm{O}\)
(vi) It oxidises alcohols to acids.
\(2 \mathrm{~K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+8 \mathrm{H}_{2} \mathrm{SO}_{4}+3 \mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{OH} \rightarrow 2 \mathrm{~K}_{2} \mathrm{SO}_{4}+2 \mathrm{Cr}_{2}\left(\mathrm{SO}_{4}\right)_{3}+3 \mathrm{CH}_{3} \mathrm{COOH}+11 \mathrm{H}_{2} \mathrm{O}\)

(a) In neutral medium
In neutral medium, it is reduced to MnO₂
\(\mathrm{MnO}_{4}^{-}+2 \mathrm{H}_{2} \mathrm{O}+3 \mathrm{e}^{-} \rightarrow \mathrm{MnO}_{2}+4 \mathrm{O}_{2}\)
(i) It oxidises H₂S to Sulphur.
\(2 \mathrm{MnO}_{4}^{-}+3 \mathrm{H}_{2} \mathrm{~S} \rightarrow 2 \mathrm{MnO}_{2}+3 \mathrm{~S}+2 \mathrm{OH}^{-}+2 \mathrm{H}_{2} \mathrm{O}\)
(ii) It oxidises thiosulphate into sulphate.
\(8 \mathrm{MnO}_{4}^{-}+3 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-}+\mathrm{H}_{2} \mathrm{O} \rightarrow 6 \mathrm{SO}_{4}^{2-}+8 \mathrm{MnO}_{2}+2 \mathrm{OH}\)
(b) In alkaline medium
The overall reaction is
\(\mathrm{MnO}_{4}^{-}+2 \mathrm{H}_{2} \mathrm{O}+3 \mathrm{e}^{-} \rightarrow \mathrm{MnO}_{2}+4 \mathrm{OH}^{-}\)
(c) In acid medium
(i) It oxidises ferrous salts to ferric salts.
\(2 \mathrm{MnO}_{4}^{-}+10 \mathrm{Fe}^{2+}+16 \mathrm{H}^{+} \rightarrow 2 \mathrm{Mn}^{2+}+10 \mathrm{Fe}^{3+}+8 \mathrm{H}_{2} \mathrm{O}\)
(ii) It oxidises iodide ions to iodine.
\(2 \mathrm{MnO}_{4}^{-}+10 \mathrm{I}^{-}+16 \mathrm{H}^{+} \rightarrow 2 \mathrm{Mn}^{2+}+5 \mathrm{I}_{2}+8 \mathrm{H}_{2} \mathrm{O}\)
(iii) It oxidises sulphide ion to Sulphur.
\(2 \mathrm{MnO}_{4}^{-}+5 \mathrm{~S}^{2-}+16 \mathrm{H}^{+} \rightarrow 2 \mathrm{Mn}^{2+}+5 \mathrm{~S}+8 \mathrm{H}_{2} \mathrm{O}\)

Potassium permanganate is prepared from pyrolusite (MnO₂).
(i) Conversion of (MnO₂) to potassium manganate
Powdered ore is fused with KOH in the presence of air, green coloured potassium manganate is formed.
\(2 \mathrm{MnO}_{2}+4 \mathrm{KOH}+\mathrm{O}_{2} \rightarrow 2 \mathrm{~K}_{2} \mathrm{MnO}_{4}+2 \mathrm{H}_{2} \mathrm{O}\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad Potassium \ manganate \ (green)\)
(ii) Oxidation of potassium manganate to (O₃) potassium permanganate
(a) Chemical oxidation
In this method, potassium manganate is treated with ozone (O₃) or chlorine to get potassium permanganate.
\(2 \mathrm{MnO}_{4}^{2-}+\mathrm{O}_{3}+\mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{MnO}_{4}^{-}+2 \mathrm{OH}^{-}+\mathrm{O}_{2}  \)
\(2 \mathrm{MnO}_{4}^{2-}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{MnO}_{4}^{-}+2 \mathrm{Cl}^{-}\)
(b) Electrolytic oxidation
In this method, aqueous solution of potassium manganate is electrolysed in the presence of alkali.
\(\mathrm{K}_{2} \mathrm{MnO}_{4} \rightleftharpoons 2 \mathrm{~K}^{+}+\mathrm{MnO}_{+}^{2-} \)
\(\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}^{+}+\mathrm{OH}^{-}\)
Manganate ions are converted into permanganate ions at anode.
\(2 \mathrm{MnO}_{4}^{2-} \rightleftharpoons 2 \mathrm{MnO}_{4}^{-}+2 \mathrm{e}^{-}\\ Green \quad \quad Purple\)
H₂ is liberated at the cathode.
\(2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_{2} \uparrow\)
The purple coloured solution is concentrated by evaporation and forms crystals of potassium permanganate on cooling.

(i) It oxidises ferrous salts to ferric salts.
 Cr₂O₇^2- + 6Fe²⁺+ 14H⁺ ⟶ 2Cr³⁺ + 6Fe³⁺ + 7H₂O
(ii) It oxidises iodide ions to iodine
Cr₂O₇^2- + 6I^-+ 14H⁺ ⟶ 2Cr³⁺ + 3I₂ + 7H₂O
(iii) It oxidises sulphide ion to sulphur
Cr₂O₇^2- + 3S^2-+ 14H⁺ ⟶ 2Cr³⁺ + 3S + 7H₂O
(iv) It oxidises sulphur dioxide to sulphate ion
Cr₂O₇^2- + 3SO₂+ 2H⁺ ⟶ 2Cr³⁺ + 3SO₄^2- + H₂O
(v) It oxidises stannous salts to stannic salt
 Cr₂O₇^2- + 3Sn²⁺ + 14H⁺ ⟶ 2Cr³⁺ + 3Sn⁴⁺ + 7H₂O
(vi) It oxidises alcohols to acids
2K₂Cr₂O₇ + 8H₂SO₄ + 3CH₃CH₂OH ⟶ 2K₂SO₄ +2Cr₂(SO₄)₃+ 3CH₃COOH + 11H₂O
(vii) It oxidises oxalic acid to CO2
2MnO₄^- + 5(COO)^2- + 6H⁺ ⟶ 2Mn²⁺+ 10CO₂ + 8H₂O
(viii) It oxidises iodide ions to iodine
2MnO4^- + 10I^- + 16H⁺ ⟶ 2Mn²⁺+ 5I₂+ 8H₂O
(ix) It oxidises sulphide ion to sulphur
2MnO₄^- + 5S^2-+ 16H⁺ ⟶ 2Mn²⁺+ 5S + 8H₂O
(x) It oxidises nitrites to nitrates
 2MnO₄^- + 5NO^2- + 6H⁺ ⟶ 2Mn²⁺+ 5NO₃^- + 3H₂O
(xi) It oxidises alcohols to aldehydes.
 2KMnO₄ + 3H₂SO₄ + 5CH₃CH₂OH ⟶ 2K₂SO₄ + 2MnSO₄ + 5CH₃CHO + 8H₂O
(xii) It oxidises sulphite to sulphate
2MnO₄^- + 5SO₃^2- + 6H⁺ ⟶ 2Mn²⁺ + 5SO₄^2- + 3H₂O

On the basis of magnetic properties, materials can be broadly classified as
(a) paramagnetic materials
(b) diamagnetic materials, besides these there are ferromagnetic and antiferromagnetic materials
(i) Materials with no elementary magnetic dipoles are diamagnetic, in other words a species with all paired electrons exhibits diamagnetism.
(ii) This kind of materials are repelled by the magnetic field because the presence of external magnetic field, a magnetic induction is introduced to the material which generates weak magnetic field that oppose the applied field
(iii) Paramagnetic solids having unpaired electrons possess magnetic dipoles which are isolated from one another.
(iv) In the absence of external magnetic field, the dipoles are arranged at random and hence the solid shows no net magnetism.
(v) But in the presence of magnetic field, the dipoles are aligned parallel to the direction of the applied field and therefore, they are attracted by an external magnetic field.
(vi) Ferromagnetic materials have domain structure and in each domain the magnetic dipoles are arranged.
(vii) But the spin dipoles of the adjacent domains are randomly oriented.
(viii) Some transition elements or ions with unpaired d electrons show ferromagnetism.

(i) The first transition metal Scandium exhibits only +3 oxidation state, but all other transition elements exhibit variable oxidation states by loosing electrons from (n-1)d orbital and ns orbital as the energy difference between them is very small.
(ii) At the beginning of the series, +3 oxidation state is stable but towards the end +2 oxidation state becomes stable.
(iii) The number of oxidation states increases with the number of electrons available, and it decreases as the number of paired electrons increases.
(iv) Hence, the first and last elements show less number of oxidation states and the middle elements with more number of oxidation states.
(v) For example, the first element Sc has only one oxidation state +3; the middle element Mn has six different oxidation states from +2 to +7. The last element Cu shows +1 and +2 oxidation states only.
(vi) The relative stability of different oxidation - states of 3d metals is correlated with the extra stability of half filled and fully filled electronic configurations. Example: Mn²⁺(3d⁵) is more stable than Mn⁴⁺(3d³).

(i) Ionization energy of transition element is intermediate between those of sand p block elements.
(ii) As we move from left to right in a transition metal series, the ionization enthalpy increases as expected.
(iii) This is due to increase in nuclear charge corresponding to the filling of d electrons.
(iv) The increase in first ionisation enthalpy with increase in atomic number along a particular series is not regular.
(v) The added electron enters (n-1)d orbital and the inner electrons act as a shield and decrease the effect of nuclear charge on valence ns electrons. Therefore, it leads to variation in the ionization energy values

(i) It is generally expected a steady decrease in atomic radius along a period as the nuclear charge increases and the extra electrons are added to the same sub shell.
(ii) But for the 3d transition elements, the expected decrease in atomic radius is observed from Sc to V, thereafter up to Cu the atomic radius nearly remains the same.
(iii) As we move from Sc to Zn in 3d series the extra electrons are added to the 3d orbitals, the added 3d electrons only partially shield the increased nuclear charge and hence the effective nuclear charge increases slightly.
(iv) However, the extra electrons added to the 3d sub shell strongly repel the 4s electrons and these two forces are operated in opposite direction and as they tend to balance each other, it leads to constancy in atomic radii.
(v) At the end of the series, d - orbitals of Zinc contain 10 electrons in which the repulsive interaction between the electrons is more than the effective nuclear charge and hence, the orbitals slightly expand and atomic radius slightly increases.

The heavier transition elements belong to fourth (4d), fifth (Sd) and sixth (6d) transition series. Their properties are expected to be different form the elements belonging to the first (3d) series due to the following reasons.
(i) Atomic radii: Size of the transition elements 94d and Sd series are larger than those of the corresponding elements of the first transition series though those of 4d and Sd series are very close to each other.
(ii) Ionisation enthalpy of Sd series are higher than the corresponding elements of 3d and 4d series.
(iii) Atomisation enthalpy of 4d and Sd series are higher than the corresponding elements of the first series.
(iv) Melting and boiling points of heavier transition elements are greater than those of the first transition series due to stronger intermetallic bonding.
(v) The elements of the first transition series generally form low or high spin complexes, depending upon the higher of ligand field. However, the heavier transition elements form low spin complexes irrespective of the strength of the ligand filed.

(i) Only the ions that have unpaired electrons in d- orbital and in which d - d transition is possible will be coloured.
(ii) The ions in which d - orbitals are empty or completely filled will be colourless as no d -d transition is possible in those configurations.
(iii) From the above ions, it can be easily observed that only Sc³⁺ has an empty d - orbital and Cu⁺ has completely filled d-orbitals.
(vi) All other ions, except Sc³⁺ and Cu⁺, will be coloured in aqueous solution because of d - d transition.