Question

(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 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 1

(a) Classification is done to study the properties of elements conveniently. 

(b) Increasing order of atomic mass and similarity in chemical properties i.e. the nature of oxide and hydride formed. 

(c) The gaps were left for undiscovered elements then. 

(d) Noble gases were not invented at that time. 

(e) Cl-35 and Cl-37 will be kept in the same slot as their chemical properties are same.