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| The Evolution Of Periodic Table |
The Evolution Of Periodic Table
Various attempts
were made by scientists to give more précised periodic table: E. g:
- Dobereiner proposed triads in 1820,
- Newlands proposed Octaves in 1860
- Mendeleev for the first time classified elements on the basis of their atomic masses in 1865.
All these
attempts mentioned above had draw backs. After the discovery of proton, proton
number built up. On the basis of which in 1913 Moseley presented an accurate
periodic table of elements. He arranged elements according to their atomic
number. As result similar elements were placed in same group and different
elements were placed in different groups. Now it is easy to understand and determine
both chemical and physical properties of elements.
The Modern periodic law? Explain with
examples.
Ans. This law states that “the physical and chemical properties
of an element are the periodic functions of their atomic number”. E. g:
- The physical and chemical properties of Alkali metals repeat after an interval. As result the Alkali metals having similar properties are placed in the same group.
- The physical and chemical properties of halogens also repeat after an interval. As result all the halogens (salt formers) are placed in the same group. And so on.
