Question

What is the basic theme of organisation in the periodic table?

Answer 1

In the periodic table, elements are classified in groups (vertical columns) and periods (horizontal rows) according to their properties. Elements with similar physical and chemical properties are placed in the same group in the periodic table.

Complete step by step answer:
By now there are 118 elements in the periodic table and with such a large number of elements it is very difficult to study the chemistry of all these elements and their innumerable compounds individually. To ease out this problem many scientists in the past searched for a systematic way to organise their knowledge by classifying the elements. Classification of elements into groups and periods, development of periodic law and periodic table are the consequences of systematising the knowledge gained by a number of scientists.

It was Dmitri Mendeleev who was responsible for publishing the periodic law for the first time. It is stated as follows:
The properties of the elements are a periodic function of their atomic weights.
Mendeleev arranged elements in horizontal rows, now called periods and vertical columns, called groups in order of their increasing weights in such a way that the elements with similar properties occupied the same vertical column or group. He fully recognized the significance of periodicity and used physical and chemical properties to classify the elements.

Later, Mendeleev’s periodic law was modified and the modified law is known as Modern periodic law. It is stated as follows:
The physical and chemical properties of the elements are periodic functions of their atomic numbers.
Elements having similar outer electronic configuration in their atoms are arranged in the same group. Thus, the basic theme of organisation of elements in the periodic table is to classify them into groups and periods.

Note: The arrangement of elements in the periodic table makes the study of elements and their compounds easy and systematic. There are a total 18 groups and 7 periods in the periodic table. The period number corresponds to the highest principal quantum number of the elements in a period.