Question

Fill in the blanks.
According to modern periodic law, the properties of elements are the periodic functions of their _____.

Answer 1

The modern periodic law was developed in order to explain the drawbacks in Mendeleev’s periodic table. According to the modern periodic law, when the elements are arranged in the increasing order of their atomic numbers, similar elements are repeated after regular intervals.

Complete step by step answer:
In order to explain the drawbacks in Mendeleev’s periodic table, there are two possibilities which appear on our mind: perhaps the arrangement of Mendeleev’s table is not a satisfactory one and perhaps the atomic mass is not a fundamental property upon which this table was based.
This was found to be true by Moseley who bombarded different elements with cathode rays and obtained X - rays of different frequencies from different elements. He found that the atomic numbers of the elements are proportional to the square root of the frequency of the X - rays. This clearly showed that there is a definite relationship between the atomic numbers and the frequency of the X - rays. Since the frequency of the X – rays emitted by each element depends upon the internal structure of the atom, the atomic number and not the atomic mass is the fundamental property of atoms. Hence, the periodic law was modified.

Hence, according to the modern periodic law, the physical and the chemical properties of the elements are the periodic function of their atomic numbers.

Note:
According to the modern periodic law, when the elements are arranged in the increasing order of their atomic numbers, similar elements are repeated after regular intervals. These regular intervals are 2, 8, 8, 18, 18, 32 and are called magic numbers.
The elements which are repeated after regular intervals are found to have similar electron configurations. Since the properties of an element depend upon its electronic configuration, this repetition of electronic configurations leads to periodicity of elements.