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Chapter No.1
Periodic Classification
Scientific Reasons
Q.l: Why modern classification is better classification?
Ans. Modern classification was prepared on the logical and scientific grounds. It corrected the position of some elements that were wrongly placed in previous periodic table. It used the empirical approach to express to periodicity of the elements with increasing atomic number.
Q.2: Why was Mendeleev's periodic law modified?
Ans. Mendeleev's periodic law was modified because.
• It doesn't have position of isotopes.
• It has alkali and coinage metals in same group.
• There was no regular difference in atomic masses of two consecutive elements.
• Lanthanides and Actinides were assigned wrong positions.
Q.3: Why every period starts from nsl and ends at ns2 np6?
Ans. In modern periodic table, s-block elements are placed on left side and p-block elements are on right side. s-block has general electronic configuration of nsl-2 and p-block has ns2 npl-6. So we can say that every period starts from nsl and ends at ns2 np6.
Q.4: Why the elements of a group in the periodic table has same valence shell configuration?
Ans. In a group of the periodic table, elements of similar characteristics are kept such as valency, number of outer most electrons, chemical characteristic etc. hence they have same valence shell configuration too.
By Practical Center
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