Question

(i) Why do we classify elements? (ii) In Mendeleev's Periodic Table, why was there no mention of noble gases like Helium. Neon and Argon?

Answer 1

i). We classify the elements to study the elements easily as a collective because there are total 118 elements which is not easy so we classify the elements into groups and periods

ii). They were not found at that time but after they were found he made a new group for them.