explain the limitations and achievements of doberenier newland and mendleev classification of elements
Answers
Limitations of mendeleev’s classification :
(i) He could not assign a correct position of hydrogen in his periodic table, as the properties of hydrogen resembles both with alkali metals as well as with halogens.
(ii) The isotopes of the same element will be given different position if atomic number is taken as basis, which will disturb the symmetry of the periodic table.
(iii) The atomic masses do not increases in a regular manner in going from one elements to the next.
Advantages of mendeleev's classification:
- Mendeleev was the first one to establish a systematic arrangement and bring out the periodicity of properties of elements with atomic weight and propose a periodic law.
- It could point out the incorrect atomic weight of some elements known at that time.
- It could predict the existence of other elements and could predict their properties so, as to leave space in the periodic table.
- It could accommodate all the sixty elements discovered at that time and could accommodate the noble gases which, where discovered later
limitations of doberenier classifaction
- Dobereiner could identify only three traids from the element known at that time.
- Not all groups obeyed the Law of Triads. For example, nitrogen family does not obey the law of triads.
Advantages doberenier
- Dobereiners research was that it made chemists look at elements in terms of groups of elements with similar chemical and physical properties.
Newland Advantages
- Newlands law of octave provided a basis for the classification of element on the basis of having similar properties into groups of elements.
- The arrangement of elements in tabular form was provided by Newlands law of Octaves.
- Newlands law of octave was the first logically basis on the atomic weight.
Limitations of Newland’s law of octaves:
- This law was applicable upto calcium only. After Ca every 8th element did not possess properties similar to that of the first.
- It was assumed by Newland that only 56 elements exist in nature and no more elements would be discovered in future. But later on several new elements were discovered whose properties did not fit into the law of octaves.
- In order to fit elements Newlands adjusted two elements in the same slot but also put some unlike elements under the same note. Example cobalt and nickel.
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Answer:
Limitations of Newland’s law of octaves:
This law was applicable upto calcium only. After Ca every 8th element did not possess properties similar to that of the first.
It was assumed by Newland that only 56 elementsexist in nature and no more elements would be discovered in future. But later on several new elements were discovered whose properties did not fit into the law of octaves.
In order to fit elements Newlands adjusted two elements in the same slot but also put some unlike elements under the same note. Example cobalt and nickel.
Limitations of Mendeléev’s periodic table:
Position of hydrogen was uncertain as it behaves like alkali metals as well as like halogens.
No place for isotopes.
Atomic masses don't increase in regular manner from one element to next. Example : V and Cr.