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Wey ah ee, , Periodic Classification of, antes, , , , Electronic configuration of Halogens, , Element Atomic Number Electronic Configuration, Fluorine 9 | 2,7, Chlorine 17 | 2,8,7, Bromine 35 | 2,8,18,7, Iodine 53 | 2,8,18,18,7, |, Astatine 85 2,8,18,32,18,7, , All the elements included in the group have seven electrons in the valence shell, of their atoms., , The resemblance in properties of the elements (particularly the chemical, properties) is because of the repetition of the same valence shell electronic, configuration., , Modern Periodic Table, , eal om) mt), , , , 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,, , = O gq