NCERT Solution for Class 10 Science Chapter 5
Periodic Classification of Elements
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-81
Questions No-2
What were the limitations of Döbereiner’s classification?
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Limitation of Dobereiner’s classification:
All known elements could not be classified into groups of triads on the basis of their
properties.
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Only 9 elements were set in the form of triads rest were not following the property of triads.
Explanation:
Döbereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.
For example, take the triad consisting of lithium (Li), sodium (Na) and potassium (K) with the respective atomic masses 6.9, 23.0 and 39.0.
Döbereiner could identify only three triads from the elements known at that time. Hence, this system of classification into triads was not found to be useful.
N: 14.0 Ca: 40.1 Cl: 35. 5
P: 31.0 Sr: 87.6 Br: 79.9
As: 74.9 Ba: 137.3 I: 126.9
He was fail to form triads for all the elements known at that time.
He can made only three triads. Rest elements were not fit in the triads.
Limitations of Dobereiner’s classification:
(i) Dobereiner could find only three triads; .i.e total of 9 elements only.
(ii) However the total number of elements were more than that of those encompassed in Dobereiner’s Triad.
(iii) Thus, Dobereiner’s could not be classify most of the elements known at that time.