The first periodic table which is named after him which included all the known elements. It consists of seven horizontal rows called periods and numbered from 1 to 7. It has nine vertical columns called groups and numbered from zero to VIII. Main achievements of Mendeleev’s periodic table were i inclusion of all the known elements and ii prediction of new elements.

Main defects of Mendeleev’s periodic table were
i position of isotopes,
ii anomalous pairs of elements like Ar and K
iii grouping of dissimilar elements and separation of similar elements.

Elements belonging to same group have same number of valence electrons and thus show same valence and similar chemical properties. Arrangement of elements in the periodic table shows periodicity. Atomic and ionic radii and metallic character increase while ionization energy, electron affinity and electro negativity decrease in a group from top to bottom. Number of valence electrons, ionization energy, electron affinity and electro negativity increase while metallic character and atomic and ionic radii decrease in a period from left to right.

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