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The long form of the periodic table has several advantages over the original Mendeleev's table. Superiority of Long Form of Periodic Table Table showing correlation between number of elements in periods and number of shells accommodating the electrons PeriodĪ) For the atoms of the elements in the same period, the electrons are added successively in the same principal shell while moving from left to right.ī) The atomic-sized of the elements generally decrease from left to right in the periodic table.Ĭ) In a period, on going from left to right, the metallic character of the elements decreases while their nonmetallic character increases.ĭ) As the electronic configuration changes along the period, the chemical properties of the elements also change. They belong to the seventh period and have the atoms which are filled with electrons in 5f sub-shell. Similarly, the elements in the second row are called actinides. These elements actually belong to the sixth period and the atoms of the elements are filled with electrons in 4f sub-shell. The elements in the first row are called lanthanides.
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The periodic table shows at the bottom of table two horizontal rows each containing 14 elements. The next three periods with 18, 18, and 32 elements are called long periods while the seventh period is an incomplete long period. The first three periods of the periodic table from the top with 2, 8, and 18 elements, respectively are known as short periods. For example, 4 thperiod contains the elements whose atoms have electrons in four different shells (i:e K, L, M, and N). In fact, there is a correlation between the period number and the number of principal shells occupied by the electrons. Different periods contain a variable number of elements. There are seven periods in the long form of the periodic table as in the original, Mendeleev's periodic table. The horizontal rows in the long form of the periodic table are called periods. In the earlier arrangement, the groups retained the same names which were assigned to them in the Mendeleev's periodic table i:e IA, IIA, IIIB to VIIB, VIII, IB, IIB, IIIA to VIIA and zero.Ī) In a group, all the elements have the same general electronic configuration of the atom.ī) The elements in a group are separated by definite gaps of atomic number (2, 1, 18, and 32).Ĭ) The atomic sizes of the elements in a group increase down the group due to the successive addition of the number of electron shells.ĭ) The elements in each group have generally similar chemical properties because they are related to the valence shell electronic configuration of the atoms.Į) The variation in physical properties of the elements such as melting point, boiling point, density, solubility e.t.c. There are 18 vertical columns in the long form of the periodic table called groups. source: Fig: Modern Periodic Table Features of Long Form of Periodic Table The widely accepted table is the extended or long form of periodic table, also known as Modern Periodic Table. Similar explanation can be offered for the periodicity of the elements present in any other group.Ī number of tables have been suggested for the classification of elements in order to eliminate the defects of Mendeleev's periodic table. This means that the same valence shell electron configuration gets repeated in a group when elements are separated by certain definite gaps of atomic numbers (8, 8, 18, 18, 32) which are also known as magic numbers. Elementġs 22s 22p 63s 23p 63d 104s 24p 64d 105s 25p 66s 1ġs 22s 22p 63s 23p 63d 104s 24p 64d 104f 145s 25p 65d 106s 26p 67s 1įrom the table above, it is quite clear that all the atoms listed have one electron (ns 1) in their valence shells. Thus, if the electrons in the outermost shell of the atoms are same, their properties will also be similar.
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Since electrons present in the inner shells do not take part in chemical combinations, it must be the electrons in the outermost shell, which control the properties of the atoms. Physical and chemical properties of the elements must be related to the arrangement of electrons in their atoms. Periodicity may be defined as the repetition of similar properties of the elements placed in a group and separated by certain gaps of atomic numbers. Thus, he defined Modern Periodic Law as the physical and chemical properties of the elements are the periodic functions of their atomic numbers. In 1913, Henry Moseley, an English physicist, by his experiment concluded that atomic number is a more fundamental property of an element and not its atomic mass.