The d- and f- Block Elements Test

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The transition metal ions which have completely filled $$d-orbitals$$ are colourless as the excitation of electron or electrons is not possible within $$d-orbitals.$$ The transition metal ions which have completely empty $$d-orbitals$$ are also colourless. In certain oxysalts of transition elements like $$KMnO_{4},\ K_{2}Cr_{2}O_{7},$$ there are no unpaired electrons at the central atom but they are deep in colour. The colour of these compounds is due to charge transfer spectrum. For example, in $$MnO_{4}^{-},$$ an electron momentarily transferred from $$O$$ to the metal and thus oxygen changes from $$O^{2-}$$ to $$O^{-}$$ and manganese from $$Mn(+VII)$$ to $$Mn(+VI).$$

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Most of the compounds of the transition metals are coloured in the solid or in solution states. The colour of the transition metal ions arises from the excitation of electrons from the $$d-orbitals$$ of lower energy to the $$d-orbitals$$ of higher energy. The energy required for $$d-d$$ electron excitation is available in the visible range. Transition metal ions have the tendency to absorb certain radiations from the visible region and exhibit the complementary colour.

The transition metal ions which have completely filled $$d-orbitals$$ are colourless as the excitation of electron or electrons is not possible within $$d-orbitals.$$ The transition metal ions which have completely empty $$d-orbitals$$ are also colourless. In certain oxysalts of transition elements like $$KMnO_{4},\ K_{2}Cr_{2}O_{7},$$ there are no unpaired electrons at the central atom but they are deep in colour. The colour of these compounds is due to charge transfer spectrum. For example, in $$MnO_{4}^{-},$$ an electron momentarily transferred from $$O$$ to the metal and thus oxygen changes from $$O^{2-}$$ to $$O^{-}$$ and manganese from $$Mn(+VII)$$ to $$Mn(+VI).$$

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Two types of magnetic behaviour are found in substances :
(a) Diamagnetism and (b) Paramagnetism

Diamagnetic substances are those which are repelled by an applied magnetic field. Such substances have no unpaired electron. Paramagnetic substances are those which are attracted by an applied magnetic field. Transition metals and many of their compounds show paramagnetic behaviour where there are unpaired electron or electrons. The magnetic moment arise from the spin and orbital motions in ions or molecules. Magnetic moment of $$n$$ unpaired electrons is given as,

$$\mu =\sqrt { n\left( n+2 \right) } $$ Bohr Magneton

Magnetic moment increases as the number of unpaired electrons increases.

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(I)A powdered substance (A) on treatment with fusion mixture $$(K_{2}CO_{3}andKNO_{3})$$ gives a green coloured compound (B) (II) The solution of (B) in boiling water in acidification with dilute $$H_{2}SO_{4}$$ gives a pink coloured compound (C) (III) The aqueous solution of (A) on treatment with NaOH and $$Br_{2}$$ water gives a compound (D) (IV) A Solution of (D) in conc $$HNO_{3}$$ on treatment with lead peroxide at boiling temperature produced a compound (E) which was of the same colour at that of (C) (V) A solution of (A) on treatment with a solution of barium chloride gave white precipitate of compound (F) which was insoluble in conc . $$HNO_{3}$$ and conc HCl.

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