Q9 of 40 Page 5

Besides gallium, which other elements have since been discovered for which gaps were left by Mendeleev in his periodic table? (any two)

Scandium (Sc) and Germanium (Ge) elements have been discovered for which gaps were left by mendeleev in his periodic table.

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7

Why was the position of hydrogen not fixed in Mendeleev's periodic table?

 8

Why do you think the noble gases are placed in a separate group ?

 10

Account for the following:

a. Cations are smaller in size than the corresponding atom.


b. The noble gases were discovered very late.

 11

The electronic configuration of four elements A,B,C and D is given as follows:

A-2,8 B-2,8,1


C-2,8,2 D-2,8,8


a. Which of them belong to the same period? Name the period.


b. Which of them belong to the same group? Name the group.