The modern periodic table
The modern periodic table was put forward by Mosley to overcome the defects of Mendeleev’s periodic table. Mosley in 1911, proposed that the physical and chemical properties of an element depend on the no. of electrons and their arrangement in different orbitals of the atom, and so the classification of the elements should be based on the number of these electrons (i.e. atomic number) and their arrangement in different orbitals.
This idea led by Mosley made most of the defects of Mendeleev’s periodic table disappear. According to the Modern periodic table ''the properties of elements are a periodic function of their atomic numbers, i.e. if the elements are arranged in the increasing order of their atomic numbers, the properties of the elements (i.e. similar elements) are repeated after definite regular intervals or periods.” Modern periodic table includes groups or periods.
The vertical columns are called groups. The total number of groups are 18 which are I A, II A, III A, IV A, V A, VII A, Zero, I B, II B, III B, IV B, V B, VI B, VII B and three columns of group VIII. The horizontal rows shown in the periodic table are called periods or simply rows. There are seven periods in the table.
General Characteristics of Groups
1.Valency Electrons : On moving down a given group the number of valency electrons does not change, i.e. remains the same.
2.Valency : The valencies of all the elements of the same group are the same.
3.Physical and Chemical Properties: All the elements of a given group possess very similar physical and chemical properties.
4.Size of Atoms : Size of atoms increases on descending a group.
5.Metallic Character : The metallic character of the elements increases in moving from top to bottom in a group.
General Characteristics of Periods
1.Valency Electrons : Number of valency electrons increases from 1 to 8 when we proceed from left to right in a period.
2.Valency : The valency of the elements with respect to hydrogen in each short period increases from 1 to 4 and then falls to one while the same with respect to oxygen increases from 1 to 7.
3.Size of Atoms : Size of atoms decreases from left to right in a period.
4.Metallic Character : On moving from left to right in a period the metallic character of the elements decreases.
5.No. of Shells : In going from left to right in a period the number of electron shells remains the same and the number of a period corresponds to the number of the shells found in the elements of that period.
This idea led by Mosley made most of the defects of Mendeleev’s periodic table disappear. According to the Modern periodic table ''the properties of elements are a periodic function of their atomic numbers, i.e. if the elements are arranged in the increasing order of their atomic numbers, the properties of the elements (i.e. similar elements) are repeated after definite regular intervals or periods.” Modern periodic table includes groups or periods.
The vertical columns are called groups. The total number of groups are 18 which are I A, II A, III A, IV A, V A, VII A, Zero, I B, II B, III B, IV B, V B, VI B, VII B and three columns of group VIII. The horizontal rows shown in the periodic table are called periods or simply rows. There are seven periods in the table.
General Characteristics of Groups
1.Valency Electrons : On moving down a given group the number of valency electrons does not change, i.e. remains the same.
2.Valency : The valencies of all the elements of the same group are the same.
3.Physical and Chemical Properties: All the elements of a given group possess very similar physical and chemical properties.
4.Size of Atoms : Size of atoms increases on descending a group.
5.Metallic Character : The metallic character of the elements increases in moving from top to bottom in a group.
General Characteristics of Periods
1.Valency Electrons : Number of valency electrons increases from 1 to 8 when we proceed from left to right in a period.
2.Valency : The valency of the elements with respect to hydrogen in each short period increases from 1 to 4 and then falls to one while the same with respect to oxygen increases from 1 to 7.
3.Size of Atoms : Size of atoms decreases from left to right in a period.
4.Metallic Character : On moving from left to right in a period the metallic character of the elements decreases.
5.No. of Shells : In going from left to right in a period the number of electron shells remains the same and the number of a period corresponds to the number of the shells found in the elements of that period.
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