MENDELEEV’S Periodic Law:

                                                                    In 1869 Mendeleev’s first published the periodic system of element on the  basis of periodic law. According to this law physical and chemical properties of elements are functions of their atomic masses”.

“The properties of elements are periodic  functions of their atomic masses”

He arranged the 63 known elements in the periodic table horizontally in the order of the their similarities in properties. The horizontal rows are called periods and verticals columns groups.

Main Characteristic of Mendeleev’s periodic Table

·         Mendeleev’s excluded certain elements and assigned them a separate position.

·         Some chemically similar elements had been placed differently for e.g., Cu, & Hg  , Ag, and Te and Ba and Pb.

·         Left gaps for the then undiscovered elements.

·         The order of atomic mass in reverse in some elements (a) Co(58.9) precedes Ni(58.6) (b) Ar(39.9) precedes K(39.1)

·         The properties of the elements vary gradually and get repeated at intervals 2.8.8.18.18.and 32 elements respectively.

·         Position of hydrogen is not clear. It demands its position on 1^st group as well in 7^th group.

·         Some chemically dissimilar elements have been placed in the same group for e.g. alkali metals (Li,Na,K—) of subgroup IA and coinage metals (Cu, Ag, Au, )of sub group IB are placed in group 1^st.

·         Predicted the existence of some undiscovered elements

·         Isotopes have no place in this periodic table.

Instruction:    Separate  advantages (merits ) and disadvantages(demerits) of Mendeleev’s periodic  from above  information

Advantages(Merits)	Disadvantages(Demerits)