(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.
a) Atomic mass
- He could classify all the 63 elements known at that time.
- He left gaps for the yet to be discovered elements.
- He predicted the properties of such elements.
c) Observations which posed a challenge
- Position of isotopes
- Irregular increase in atomic masses in going from one element to the next, making the prediction of undiscovered elements difficult.
- Position of Hydrogen.