Question

(a) Why did Mendeleev left gaps in his periodic table? 

(b) State any three limitations of Mendeleev’s classification. 

(c) How does electronic configuration of atoms change in period with increase in atomic number?

Answer 1

(a) Mendeleev left some gaps for undiscovered elements, because he predicted that there would be such elements which will fit in the gaps in future. He also predicted the properties of these elements. 

(b) Three limitations are. 

• Position of hydrogen was not justified. 
• Increasing order of atomic mass could not be maintained. 
• Isotopes were not given separate place as they have different atomic mass. 

(c) In a period, the inner core shell remains same and the valence electrons in valence shell goes on increasing from left to right. The number of shells is same.