Question

How do the early attempts to classify the chemical elements differ from the modern attempt? Which of the two is better and why? Give examples.
(class 10 CBSE SAMPLE PAPER 2017-18 SCIENCE)

Answer 1

The early attempts to classify elements were made on the basis of atomic masses of the elements. Modern basis for the classification of element is the atomic number of elements. Modern Periodic table is  better because now it is established that atomic number of an element is the fundamental property. Further there are certain anomalies in Mendeleev's periodic table such as the position of isotopes and misplacements of certain elements for e.g both isotopes of chlorine Cl- 35 and Cl- 37 can neither be placed in the same not in the different slot In The Mendeleev's periodic table.Argon is placed (atomic number =18 ,atomic mass= 40) before potassium in Mendeleev's periodic table (atomic mass= 39 and atomic number= 19).

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