Question

list two reasons responsible for late discovery of noble gases because of noble gases did not find place in Mendeleev periodic table?

Answer 1

Two reasons responsible for late discovery of noble gases are:-

i) Noble gases are available in extremely low concentrations in our atmosphere.

ii) They are very inert (chemically inactive).

Noble Gases were not included in the Mendeleev Periodic Table as they were not discovered at that time. Moreover, unlike most elements, Mendeleev could not predict their existence. This is because Mendeleev would have no clear reason to suspect there were missing elements when they can be separated by multiple units. But he did notice trends, and was able to predict some holes based on those trends. The entire column of noble gases, though, could be missed because it was a periodic gap, not a gap in the period.