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Explain the position of lanthanoids in the periodic table. |
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Answer» Solution :(1) Position of Lanthanoids in the periodic table : `"Group - 3,PERIOD - 6".` (2) They interrupt the third transition series of d-block elements (i.e. 5d series) in the sixth period. (3) They are 14 elements from `._(58)Ce` to `._(71)Lu` and their positon is in between La and Hf. Since they follow lanthanum, they are called lanthanoids. (4) They are called 4f-series elements and for the convenience they are placed separately below the main periodic table. (5) Actual position of lanthanoids is in between Lanthanum (Z = 57) and Hafnium (Z= 72). (6) Their position is justified due to following reasons. : (i) All these elements have the same electronic configuration in ULTIMATE and penultimate shells, one electron in 5d-orbital and two electrons in 6s-orbital. (ii) Group valence of all lanthanoids is 3. (iii) All lanthanoids from `._(58)Ce` to `._(71)Lu` have smiliar physical and chemical properties. |
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