(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.