Why did Mendeleev left gaps in his periodic table ?

(a) Why do we classify elements ? (b) What were the two criteria used by Mendeleev in creating his Periodic Table ? (c ) Why did Mendeleev leave some gaps in his Periodic Table? (d) In Mendeleev's Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon? (e ) Would you place the two isotopes of chlorine , Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same ? Justify your answer.

............. (Mendeleev / Moseley) left gaps in the periodic table for the undiscovered elements.

What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev’s Periodic Law.

What were the criteria used by Mendeléev in creating his Periodic Table?

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

The property used by Mendeleev to classify the elements in his periodic table is "________" .

Which group of elements was missing from Mendeleev.s original periodic table ?

The number of elements known in Mendeleev's presented periodic table is:

How many periods and groups were present in Mendeleev's original periodic table?