Question

Mendeleves peroidic table all demrit andmerit ??

Answer 1

Answer:

Uses of Mendeleev's periodic table :

•Atomic weights of elements were determined with the help of periodic table. Atomic weight=valency×equivalent weight

• Atomic weights of elements were corrected. Atomic weight of Be was calculated to be 3×4.5=13.5 by considering valency 3, but mendeleev calculated it to be 2×4.5=9.

• Discovery of new elements: In mendeleev's periodic table two consecutive members differ by two or three units in the atomic weight. Where this gap was more, the gaps were left in the periodic table.

• The discovery of the first two noble gases helium (He) and argon (Ar) in 1890 suggested the posibilities that there must be other similar elements to fill an entire family. This idea led Ramsay to his successful search for krypton (Kr) or xenon (Xe) .

• Work on the radioactive decay series for Uranium (U) and Thorium (Th) was also guided by the periodic table.

Defects of Mendeleev's periodic table:

The following is a list of defects:

• Position of hydrogen is uncertain. It has been placed in 1stA and 7th A groups because of its resemblance with both the groups.

• No seperate positions for isotopes.

•No seperate group for lanthanides and actinides .

• Although there is no resemblance expect valency of subgroups A and B , they have been put in the same group.

•The order of increasing atomic weights is not strictly followed in the arrangement of elements in the periodic table. For example, Co( At.wt.58.9)

is placed before Iodine (At.wt.127) and At(At.wt.39.9) before K(At.wt.39).