Unit 3: Periodicity

Classification of Elements and Periodicity in Properties

​11CBSE: Chemistry

1. Law of Triads (Johann Dobereiner):

   Middle element of each of the Triads had an atomic weight about halfway between the atomic weights of the other two.

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Genesis of Periodic Classification

2. Law of Octaves (John Alexander Newlands):

   Every eighth element had properties similar to the first element.

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Genesis of Periodic Classification

The properties of the elements are a periodic function of their atomic weights.

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The physical and chemical properties of the elements are periodic functions of their atomic numbers.

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Mendeleev's Periodic Law