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(a) List any three observations which posed a challenge to Mendeleev’s Periodic law.(b) How does the metallic character of elements vary on moving from(i) left to right in a period,(ii) from top to bottom in a group of the Modem Periodic Table?Give a reason for your answer.
(a) The three observations that challenged Mendeleev's Periodic Law were:
- Arranging elements according to the increasing order of atomic mass could not be maintained. Chemical properties do not depend on atomic mass.
- Isotopes were not given any place in the table as they have different atomic mass but the same chemical properties.
- A correct position could not be assigned to hydrogen in the periodic table.
(b) (i) On moving from left to right in a period, the metallic character of elements decreases because electropositive character decreases.
(ii) Ongoing down in a group of the periodic table, the metallic character of elements increases because of the electropositive character of elements increases.
Updated on: 10-Oct-2022
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