Periodic Classification of Elements (C10)

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

(b) List two achievements of Mandelẽev’s periodic tables.

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

Answer

a) Atomic mass

b) Achievements

  1. He could classify all the 63 elements known at that time.
  2. He left gaps for the yet to be discovered elements.
  3. He predicted the properties of such elements.

c) Observations which posed a challenge

  1. Position of isotopes
  2. Irregular increase in atomic masses in going from one element to the next, making the prediction of undiscovered elements difficult.
  3. Position of Hydrogen.