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Question

Mention the contribution of Mendeleev's periodic table. What are the drawbacks of Mendeleev's periodic table?

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Solution

In 1869, just five years after John Newlands put forward his law of octaves, a Russian chemist called Dmitri Mendeleev published a periodic table. Mendeleev also arranged the elements known at the time in order of relative atomic mass, but he did some other things that made his table much more successful.

He realised that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table

Sometimes this method of arranging elements meant there were gaps in his horizontal rows or 'periods'. But instead of seeing this as a problem, Mendeleev thought it simply meant that the elements which belonged in the gaps had not yet been discovered.

He was also able to work out the atomic mass of the missing elements, and so predict their properties. And when they were discovered, Mendeleev turned out to be right. For example, he predicted the properties of an undiscovered element that should fit below aluminium in his table. When this element, called gallium, was discovered in 1875, its properties were found to be close to Mendeleev's predictions. Two other predicted elements were later discovered, lending further credit to Mendeleev's table.

Contributions

1) He first classified the periodic table into groups and periods.

2) Elements resemble the same property at fixed interval.

Drawbacks

Disadvantages :-
1. Couldn't explain position of Hydrogen
2.Couldn't answer the question "Can we have an element with atomic mass 3 between Hydrogen and Helium
3 He placed cobalt before Nickel though Cobalt has more mass


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