Question

Can anyone give me some demerits of dobereiner's triads & newland's octaves please??

Answer 1

Drawbacks of Dobereiner’s classification of elements was that it failed to arrange all the then known elements in the form of triads of elements having similar chemical properties. His classification was not applicable to all known elements but was limited only to a few elements. For example: nitrogen, Phosphorus and arsenic have similar chemical properties but they do not constituent a Dobereiner’s triad.  Dobereiner’s could identify only three triads from the elements known at that time. So his classification of elements was not much successful. Dobereiner also failed to explain the relation between atomic masses of elements and their chemical properties.


Drawbacks of  Newlands law of octaves :1.The law of octaves worked well only for letter elements and could not be extended to Elements atomic mass is higher than that of calcium.2. Newlands assume that only 56 elements existed in nature with no scope for discovery of the elements in future. Subsequently, quite a large number of new elements were discovered whose properties did not fit into Newlands’ law of octaves.3. Newlands assign one position to two elements in order to fit the elements in his periodic table. For e.g only one position each was assigned to (Co & Ni) & (Ce & La).4. Newlands placed Cobalt(Co) and Nickel(Ni) in the same column as F, Cl & Br having quite different properties in comparison to Cobalt (Co ) and Nickel(Ni).5. Newlands placed Fe far away from Co and Ni although Fe resembles Co and Ni in properties.
HOPE THIS WILL HELP YOU...