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Mendeleeve first made periodic table but there were many shortcomes as follows.
Elements Ni nickel and Co cobalt were having same whole atomic mass. Therefore there was confusion about there position.
Isotopes were discovered very long after Mendeleeve put fotrth periodic table. A problem was faced in placing them in periodic table.
After taking all these things in mind modern periodic table was made.
structure of modern periodic table is as followa.
It is consist of 118 elements
7 periods
18 groups
characteristics are as follows
atomic radius of element decreases as we go from left to right in periodic table due to increase in inward pull of nucleus.
hope it helps u
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