Question

EXPLAIN THE CLASSIFICATION and ALSO state ALL the DRAWBACKS of

1)NEWLAND



2)DOBEREINER



3) MENDELEEV


EACH BRAINLY MEMBER DO EACH SCIENTIST'S DRAWBACKS.



NO SMALL ANSWERS AND SPAM.

Answer 1

drawbacks of mendeleev 's periodic table
*position of hydrogen is not clear.
*position of isotopes is also not clear in his periodic table .
*lots of these elements with higher atomic weight have been placed before the one with lower atomic weight . e.g. co [wt. 58.9] precedes Ni [ wt. 58.7].

Answer 2

1) By the time of Newland 56 elements were discovered. He classified them on the basis of atomic mass. Newland's law state that 'When elements are classified on the basis of atomic mass,the properties of the eight element is similar to the first'
Drawbacks:
1) Newland could identify element only up to calcium out of 56 elements known.
2) After 56 elements every eight element did not possess properties similar to the first.
3)Later on several elements were discovered and to fit them he placed two elements in same place which totally differed in the property.
4) Inert gasses were not included as they were not discovered.

2)Dobereiner law's state that ' In a triad,the atomic mass of middle element is approximately the mean of the atomic masses of the other two'
Drawbacks:
1)Dobereiner could identify only some of the traids from the elements known.
2) Other triads did not obey Dobereiner's rule.

3)Mendeleev's law states that 'The physical and chemical properties of the elements are a periodic function of their atomic masses'. Mendeleev was the first to identify all the 63 elements discovered.
Drawbacks:
1) Hydrogen resembles both alkali as well as halogens. Therefore no fixed position could be given to hydrogen.
2) Isotopes of the same elements have different atomic mass hence they should be given different position. On the other hand isotopes are chemically similar,they had to be given same position.
3)Some elements of higher atomic mass are placed before those elements having low atomic mass. For eg. Cobalt (58.93) is placed before Nickel (58.71)
4) Manganese is placed with halogens which totally differed in the properties.