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Periodic Classification of Elements : Complete Set of Questions


This set of questions contains all the possible concepts
which could be asked in the examination

Earlier Attempts to classify Elements

Q.1 What was Dobereiner’s basis for classification of elements?

Dobereiner grouped the elements with similar chemical properties into three elements each called 'Triads'. The unique feature of a triad was the atomic mass of the middle element. When elements were arranged in order of their increasing atomic mass, the atomic mass of the middle element was approximately the arithmetic mean of the other two elements of the triad.


Q.2 What are the different triads that Dobereiner could identify?

Dobereiner's Triads are as follows:-


Q.3 What were the limitations of Dobereiner’s classification?

The major limitation of Dobereiner’s classification was that this was only applicable for some elements.

Only a limited number of elements could be arranged in triad form. 


Q.4 Write down Newlands’ law of octaves?

Newlands’ law of octaves state, “When the elements are arranged in the order of increasing atomic weights, then every eighth element has properties similar to that of the first element”

For e.g., if we start from lithium and arrange elements in ascending order of their atomic masses, the eighth element will be sodium.Both elements shows similar physical and chemical properties.


Q.5 Newlands’ octaves do not contain inert gases. Give reason?               

The inert gases were not known at that time and werediscovered later. Hence, they were not present in Newlands’ octaves.


Q.6 What were the limitations of Newlands’ law octaves?

The limitations of Newland‘s law of octaves are as follows:-

- Similarity in properties of elements as per the law was seen only up to calcium.

- At many places , two elements were put together at the same place.eg Co and Ni

- Fe having property similar to Co and Ni, was placed very far from them.

- All the elements discovered that time could not be classified into octaves.


Q.7  Up to which element, the law of octaves was found to be applicable?

The law of octaves was found applicable only up to calcium.



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