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(i) The long form periodic table (1984) consists of 18 vertical columns and 18 groups. These groups are numbered 1 to 18 from the left, using Arabic numerals.
(ii) Elements of the groups 1 and 2 , and groups 13 to 17 are called main group elements. These are also called typical or representative or normal elements.
(iii) The elements of the groups 3 to 12 in the middle of the periodic table are called transition elements.
(iv) Elements with atomic numbers 58 to 71(Ce to Lu) occurring after lanthanum are called lanthanides.
(v) Elements with atomic numbers 90 to 103(Th to Lr) are called actinides.