write a short note on mendeleev's periodic law?
Answers
Mendeleev realized 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.
Gaps and predictions 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 aluminum 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.
Mendeleev's Periodic table .
→ When Mendeleev started his work , 63 elements were known at that time .
→ He examined the relationship between the atomic masses of the elements and their physical and chemical properties .
→ Mendeleev concentrated on the compounds formed by elements with oxygen and hydrogen .
Classification criteria :-
1. The formulae of the hydrides and oxides formed by an element were treated as one of the basic properties of an element foe its classification.
2. He then took 63 cards and on each cards he wrote down the properties of one element. He sorted out the elements with similar properties and pinned the cards todether on the wall .He observed that most of the elements got a place in the periodic table and were arranged in the order of increasing atomic masses .
On this basis , Mendeleev formulated a periodic law .
→ Which states that " The properties of elements are the periodic function of their atomic masses .
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