Question

what about the gap which is after "H"?

why there is gap from group 2 period 1 to group 8 period 1 in Mendeleev's periodic table ??

Answer 1

Since hydrogen contains the properties of Group 1 and helium that of group 8 ,thus they were placed in the these groups.
Mendeleev in his periodic table could not justify the position of Hydrogen.This was one of the limitation of mendeleev periodic table.