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(Se ah ee, , ei, , Periodic Classification of, antes, , , , Modern Periodic Table, , aed om) em et), , , , Modern Periodic Table is based on the Modern Periodic Law. The elements are, arranged in order of increasing atomic numbers., , (1) Groups: There are eighteen (18) groups in the Modern Periodic Table. These, are numbered from 1 to 18., , (1) The elements present in a group are separated by definite gaps of atomic, numbers (8, 8, 18, 18, 32)., , (2) The elements present ina group have the same number of electrons in the, valence shell of their atoms., , (3) The elements present in a group have identical chemical properties., , (4) The physical properties of the elements in group such as melting point,, boiling point, density vary gradually., , (5) Atomic radii of the elements present in a group increase downwards., , (2) Periods: Modern Periodic Table has seven (7) periods also called horizontal, rows,, , (1) First period has two elements and is called short period., , (2) Second & third periods have eight elements and are also called short, periods., , (3)Fourth and fifth periods have eighteen elements and are called long periods., , (4)Sixth and seventh periods have thirty two elements and are also called long, periods., , The important characteristics of the elements in a period, , (1) In all the elements present ina period, the electrons are filled in the valence, shell., , (2) As the number of electrons in the valence shell change, the chemical, properties of the elements present ina period also change., , (3) Atomic radii of the elements in a period decrease from left to the right., , (4) Along a period, the metallic character of the elements decreases and the, non-metallic character increases., , (5) Along a period, the reducing character of the elements decreases and their, oxidising character increases., , Advantages of the Modern Periodic Table, , = O gq