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History of classification (in Hindi)
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History of the periodic table

Shaillee Kaushal is teaching live on Unacademy Plus

Shaillee Kaushal
Faculty in Chemistry with a teaching experience of 14 years. Specialised in teaching for boards and competitions.

Unacademy user
Sir I have a question Q- sin1°sin2°sin3°....sin179°sin180°= ❓ this question relative to Delhi polytechnic (CET)
  1. IIT JEE physical


  2. CLASSIFICATION OF ELEMENTS AND PERIODICITY OF PROPERTIES In short basic object of classification is to arrange the facts regarding elements and their compounds in such a way so that we may have greatest control over their characteristics with least possible effort. Attempts were made to classify the elements according to one property or the other. After the establishment of Dalton's atomic theory the chemists took atomic mass as the fundamental property and tried to find a relationship between properties of the elements and their atomic masses. The arrangement of elements in order of increasing atomic masses, with elements having similar properties in vertical columns, is called periodic table


  3. 1. Dobereiner's law of triads. Dobereiner gave his law of triads in 1815 to 1829 According to this law in certain triads the atomic mass of the central element was the anthematic mean of the atomic masses of other two elements and the property of the middle element were in between those of the end members. Some of the triads are given below: Li=7 CI = 35.5 Na 23 K 39 I 127 Br=80 mean = 81.25 Ca 40 Sr 88 Ba 137 mean 40+137 -88.5


  4. Newland's law of octaves:- He proposed his arrangment in 1864 He presented the law of octaves. The elements when arranged in order of increasing atomic masses, the eighth succeeding element was the repetition of the first one like 8th note of the musical scale. Musical Scale 1st Sa Re Ga Ma Pa Dha Ni LiBe B CNO F Na Mg Al Si P S Cl K Ca Cr Ti Mn Fe


  5. 1. Lother Meyer's arrangement Lother Meyer and Mendleev gave identical classification of elements. Both these classifications co-related atomic masses with periodicity Mendleev's classification was based on consideration of chemical properties while Lother Meyer presented the classification based on the physical properties Lother Meyer presented the classification in the form of curve while Mendleev in the form of table. Lother Meyer calculated the atomic volumes by the followng formula: Atomic volume - Atomic mass Density


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