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Compare the general characteristics of the first series of the transition metals with those of the seconds and third series metals in the respective vertical columns. Give special emphasis on the following points. (i). Electronic configuration and (ii). Oxidation states. (iii) ionisation enthalpies and (iv) Atomic. |
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Answer» (i). Electronic configuration: The elements in the same vertical column generally have similar electronic configuration However the first series shows only two exceptions, `i.e.,Cr=3d^(5)ds^(1)` and `Cu=3d^(10)4s^(1)` but second series shows more exceptions e.g., `Mo(42)=4d^(5)5s^(1),Tc(43)=4d^(6)5s^(1),Ru(43)=4d^(7)5s^(1),Rh(44)=4d^(9)5s^(1),Pd(46)=4d^(10)5s^(0),Ag(47)=4d^(10)5s^(1)`. Similarly in the third series, `W(74)=4d^(4)6s^(2),Pt(78)=5d^(9),6s^(1)` and `Au(79)=5d^(10)6s^(1)`. Thus in the same vertical column in a number of cases, the electronic configuration of the three series are not similar. (ii). Oxidation states: The elementws in the same vertical column generally show similar oxidation states. The number of oxidation states shown by the elements in the middle of each series is maximum and minimum at the extreme ends. (iii). Ionisation enthalpies: `IE_1` in each series generally increase gradually along the series though some exception are observed in each series. `IE_1` of some elements in the second `(4d)` series are higher while some of them have lower value than the element of `3d` series in the same vertical column. However, the `IE_1` of third `(5d)` series are higher than those of `3d` and `4d` series. This is because of poor shielding of nucleus by `4f` electrons in the `5d` series. (iv). Atomic sizes: In general ions of the same charge or atoms in a given series hwo progeressively decrease in radius with increasing atomic number though the decrease is quite small. But the size of the of the atoms of the atoms of `4d` series is larger than the corresponding elements of the `3d` series whereas those of corresponding elements of the `5d` series nearly the same as those of `4d` series because of lanthanoid contraction. (v). Enthalpies of atomisation: The metals of the second and third series have greater enthalpies of atomisation than the corresponding elements of the first series. This is due to much more frequent metal-metal bonding in compounds of heavy transition metals. |
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