give notes on chapter Modern periodic table (11th std)
Answers
Answer:
modern periodic table was introduced by mendeleev's in this he determine that if we put elements in the increasing order of their atomic number then a well defined periodic table can be formed
Modern Periodic Law:
In the year 1913, Henry Moseley, a young physicist from England studied the frequencies of the X-rays which were emitted when certain metals were bombarded with high speed electrons. He found that in all the cases, the square root of the frequency was directly proportional to the atomic number of the atom of the metal. He further stated that there was no co-relation between the frequency and the atomic mass.
When Moseley plotted a graph between square root of frequency and atomic numbers of different metals, a straight line was obtained. But it was not the case when a graph was plotted between square root of frequency and atomic masses of the metals. These studies led Moseley to believe that atomic number and not the atomic mass is, the fundamental property of an element.
According to him, atomic numbers must form the basis of the classification of the elements in the periodic table.
Moseley gave the Modern Periodic Law which states that: Physical and chemical properties of the elements are the periodic function of their atomic numbers.
Atomic mass of an element is due to the mass of protons and neutrons present in the nucleus of its atom.
As the number of electrons in an atom are given by the atomic number and not by the mass number therefore, atomic number should form the basis of the classification of the elements in the periodic table and not atomic mass as predicted by Mendeleev.
