Question

what are the merits-demrits of mendeleev's periodic table?

Answer 1

Merits of mendeleev's periodic table are :
1. To give proper place in the periodic table, atomic masses of some elements were revised in accordance with their property. Eg, the previously determined atomic mass of beryllium was changed to correct value 9.4 and beryllium was placed before boron.
2. When noble gas such as helium, neon, argon were discovered, Mendeleev created the zero group without disturbing the original periodic table in which the noble gases were placed very well.
Demerits :
1.The elements cobalt and nickle have same whole number atomic mass. As remit there was an ambiguity regarding sequence in mendeleev's periodic table.
2 . isotopes were discovered long time after Mendeleev put forth the periodic table. A challenge was posed in placing isotopes in mendeleev's periodic table.