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Question
Justify the position of lanthanides and actinides in the periodic table.
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Solution
Lanthanides:
1. The actual position of lanthanides in the periodic table is group number 3 and period number 6.
2. In the sixth period, the electrons are preferentially filled in the inner 4f sub shell.
3. The fourteen elements following lanthanum (Ce to Lu) show similar chemical properties.
4. Hence they are grouped together and placed at the bottom of the periodic table.
5. This position is justified as follows:
- General electronic configuration: [Xe] 4f1-14 5d0-1 6S2
- Common Oxidation state: +3
- They have similar physical and chemical properties.
Actinides:
1. The actual position of actinides in the periodic table is group number 3 and period number 7.
2. In the seventh period, the electrons are preferentially filled in the inner 5f Sub shell.
3. The fourteen elements following actinides (Th to Lr) show similar chemical properties.
4. Hence they are grouped together and placed at the bottom of the periodic table.
5. This position is justified as follows:
- General electronic configuration: [Rn] 5f2-14 6d0-2 7S2
- Common oxidation state: +3
- They have similar physical and chemical properties.
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