Question

Question 3.2 Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

Class XI Classification of Elements and Periodicity in Properties Page 92

Answer 1

The most important property did by Mendeleev : the chemical and physical properties of elements are periodic function of their atomic weight. Mendeleev used atomic weight as the basis of classification of elements in the periodic table. He arranged 63 elements known at that time in the periodic table by the basis of the order of their atomic weight and he placed elements with similar nature in same group.

He stuck to this basis sincerely as some places were left vacant for new elements which were not discovered at that time.
For example : Ga and Ge were not known at that time . he left vacant space for them and named them as eka - aluminum and eka silicon respectively. He predicted not only the existence of these two elements but also described some of their general physical properties. these elements were discovered later.

He also found some elements that didn't fit in his scheme of classification on the basis of atomic weight. in such cases , he ignored the order of atomic weight . example : iodine is placed after tellurium due to it's similar in properties with other halogens although it's atomic weight is lower than that of Tellurium.

Answer 2

Mendeleev used atomic weight as the basic classification of elements in the periodic table. he arranged the then known elements in order of increasing atomic weight grouping together elements with similar properties. he sincerely strict to his basic leaving out blank spaces where elements were not known at that time. for example, the elements gallium after aluminium and Germanium after Silicon where not known at that time mendeleev prepared his periodic table. he called then elements as a eka-aluminium and Eka- Silicon. later, these elements were discovered and their properties were found to be similar to those predict by The Mendeleev.