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Modern periodic law

Modern periodic law:
"The physical and chemical properties of the elements are the periodic function of their atomic numbers.
Cause of periodicity:The properties of an element depend upon the number of electrons present in the valence shell.The elements belonging to the same group have similar outer electronic configuration and thus they have similar properties.For example,all the alkali metals which have similar properties have similar electronic configuration of the outer most shell i.e.,ns1(where n is outermost shell).Thus,it is because of similarity in electronic configuration that all the elements have similar properties.Hence the periodic repetition of properties of the elements i.e., periodicity is due to the repetition of similar outer electronic configuration.
Magic numbers:
The elements with similar properties repeat themselves after certain intervals of 2,8,8,18,18 and 32.These numbers are known as magic numbers.

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