Grade-XI Final exam Timetable

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XI Chemistry ( Periodic table)

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Classification of Elements and Periodicity in Properties Class 11 Notes Chemistry Chapter 3 • Genesis of Periodic Classification Dobereiner’s Triads In 1829, Dobereiner arranged certain elements with similar properties in groups of three in such a way that the atomic mass of the middle element was nearly the same as the average atomic masses of the first and the third elements. A few triads proposed by him are listed. Limitations of Dobereiner’s Trids The triads given by Dobereiner were helpful in grouping some elements with similar characteristics together, but he could not arrange all the elements known at that time into triads. • Newlands’ Law of Octaves John Newlands proposed the law of octaves by stating that when elements are arranged in order of increasing atomic masses, every eighth element has properties similar to the first. Newlands called it law of octaves because similar relationship exists in the musical notes also. This can be illustrated as: Limitations of Newlands’ Law...
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