Answer:
In Dobereiner’s triads, elements were placed :
- According to increasing order of their atomic masses.
- Into groups which have similar chemical and physical properties.
- In each group there were three elements.
In Modern periodic table, elements are placed:
- According to increasing order of their atomic numbers.
- Into groups and these groups are assigned according to the numbers of valence electrons present in their valence shell.
Aspects of Dobereiner’s triads agreed with the modern periodic table
- Element of the same group will have similar chemical and physical properties.
Disagreement with the modern periodic table.
- Not all groups obeyed law of triads.
- On the basis of properties all known elements could not be classified into groups of triads.
