(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: 
  1. Arranging elements according to the increasing order of atomic mass could not be maintained. Chemical properties do not depend on atomic mass. 
  2. Isotopes were not given any place in the table as they have different atomic mass but the same chemical properties.
  3. 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.


Simply Easy Learning

Updated on: 10-Oct-2022


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