In the modern periodic table, there are seven periods and eight main groups.
Each group is sub-divided into ‘A’ and ‘B’ sub-groups.
Elements of Sub-Group ‘A’:
Elements of subgroup ‘A’ are called main or representative elements.
Elements of SubGroup ‘B’:
Elements of SubGroup ‘B’ are called Transition elements.
Lanthanides are a group of 14 elements in the 5th period. They are placed at the bottom of the periodic · table. Their electronic configurations display backfilling of 4 f level.
Actinides are also a group of 14 elements in 7th period. They are radioactive element and display filling of Sf level. They are also placed at the bottom of the periodic table.
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