NCERT Class 11 Solutions: Classification of Elements and Periodicity (Chapter 3) Exercise 3– Part 1
What is the basic theme of organisation in the periodic table?
As shown in below figure of the periodic table, the basic theme of elements organize the elements in periods and groups according to their properties.
This type of arrangement of elements make the learning of elements and their compounds simple and methodical.
In the periodic table, the elements with similar properties are also located in the same group.
Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?
In Mendeleev’s periodic table, he arranged the elements in his periodic table ordered by atomic weight or mass. He set the elements in periods and groups in order of their increasing atomic weight. He placed the elements with similar properties in the same group.
However, he did not stick to this arrangement for long. He found out that if the elements were arranged strictly in order of their increasing atomic weights, then some elements did not fit within this scheme of classification.
Therefore, he ignored the order of atomic weights in some cases. For example, the atomic weight of iodine is lower than that of tellurium. Still Mendeleev placed tellurium (in Group VI) before iodine (in Group VII) simply because iodine’s properties are so similar to fluorine, chlorine, and bromine.
What is the basic difference in approach between the Mendeleev’s Periodic Law and the Modern Periodic Law?
The basic difference between the Mendeleev’s periodic low and the modern periodic low is their physical and chemical properties of elements are periodic function of their atomic weight and atomic number.
Mendeleev’s periodic law: The physical and chemical properties of element are periodic functions of their atomic weight
Modern periodic law - The physical and chemical properties of element are periodic functions of their atomic number