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प्रश्न
Which of the following cations are coloured in aqueous solutions and why ?
Sc3+, V3+, Ti4+, Mn2+ (At. Nos. Sc = 21, V = 23, Ti = 22, Mn = 25)
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उत्तर
The color of cations is dependent on the number of unpaired electrons present in d-orbital. The electronic configuration of the following cations is as follows:
Sc (Atomic number 21) = 3d1 4s2 and Sc3+ = 3d0 4s0. As d-orbital is empty, it is colourless.
V (Atomic number 23) = 3d3 4s2 and V3+ = 3d2 4s0. As d-orbital is having 2 unpaired electrons, it undergoes d-d transition and shows green colour.
Ti = (Atomic number 22) = 3d2 4s2 and Ti4+ = 3d0 4s0. As d-orbital is empty, it is colourless.
Mn = (Atomic number 25) = 3d5 4s2 and Mn2+ = 3d5 4s0. As d-orbital is having 5 unpaired electrons, it shows pink color.
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संबंधित प्रश्न
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`(iii) 2MnO_4^-+5C_2O_4^(2-)+16H^+ ->`
|
`E_((M^(2+)/M)` |
Cr | Mn | Fe | Co | Ni | Cu |
| -0.91 | -1.18 | -0.44 | -0.28 | -0.25 | -0.34 |
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The transition metals when exposed to oxygen at low and intermediate temperatures form thin, protective oxide films of up to some thousands of Angstroms in thickness. Transition metal oxides lie between the extremes of ionic and covalent binary compounds formed by elements from the left or right side of the periodic table. They range from metallic to semiconducting and deviate by both large and small degrees from stoichiometry. Since electron bonding levels are involved, the cations exist in various valence states and hence give rise to a large number of oxides. The crystal structures are often classified by considering a cubic or hexagonal close-packed lattice of one set of ions with the other set of ions filling the octahedral or tetrahedral interstices. The actual oxide structures, however, generally show departures from such regular arrays due in part to distortions caused by packing of ions of different size and to ligand field effects. These distortions depend not only on the number of d-electrons but also on the valence and the position of the transition metal in a period or group.
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