Periodic Classification of Elements
Limitations of Mendeleev’s periodic table
- It failed to explain the position of hydrogen.
- It was not able to explain the position of isotopes.
- In the table some elements having higher mass were kept before the elements having lesser atomic mass.
Modern periodic law states that the properties of elements are a periodic function of their atomic numbers, not their atomic masses.
The modern periodic table consists of 7 periods and 18 groups. Elements having the same valence shell are present in the same period. Elements having the same number of valence electrons are present in the same group. Metals are present on the left-hand side of the periodic table, whereas non-metals are present on the right hand side of the periodic table.
Group 1, 2 and 13-18: Representative elements
Group 3-12: Transition elements
Period 6: Elements with atomic numbers 58-71: Lanthanoids
Period 7: Elements with atomic numbers 90-103: Actinoids
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