Question 2 - Past Year - 5 Mark Questions - Chapter 5 Class 10 - Periodic Classification of Elements

(a) What was the basis of Mendeleev’s classification of elements?

(b) List two achievements of Mendeleev’s Periodic table.

(c) List any two observations which posed a challenge to Mendeleev’s periodic law.

Answer

(a)

Mendeleev classified elements according to their atomic masses .

(b)

• Mendeleev was able to classify all the 63 elements that had been discovered at that time.
• He left gaps for the elements yet to be discovered and also predicted their properties.

(c)

• Since Mendeleev arranged the elements according to their atomic masses, the position of isotopes (which have the same mass number but different atomic number) could not be decided.
• The position of Hydrogen could not be decided.
• Since the atomic mass increases irregularly from one element to the next, this makes it difficult to predict the position of undiscovered elements.