Explain Mandeleev's periodic table.
Answers
Introduction to Mendeleev Periodic Table:
Mendeleev treated formulae of hydrides and oxides as one of the basic criteria for categorization. He took 63 cards and on each card, he wrote the properties of one element. He grouped the elements with similar properties and pinned it on the wall. He observed that elements were arranged in the increasing order of atomic mass and there was the periodic occurrence of elements with similar properties.
Merits of Mendeleev Periodic Table:
⇒ Some gaps were left for the elements yet to be discovered. Thus, if a certain new element is discovered, it can be placed in a new group without disturbing any existing group.
Demerits of Mendeleev Periodic Table:
⇒ He was unable to locate hydrogen in the periodic table.'
⇒ Increase in atomic mass was not regular while moving from one element to another. Hence, the number of elements yet to be discovered was not predictable.
⇒ Later on, isotopes of elements were found which violated Mendeleev’s periodic law.
mendeleef arranged the elements in the increasing order of their atomic masses in horizontal draws till he came across an element whose properties wear similar to those of the first element then he placed this element below the first element and thus started the second draw of elements .
the success of Mendeleev's classification was due to the fact that he laid more emphasis on the properties of elements rather than on atomic masses .occasionally , he could not find the element that would fit in a particular position . he left search position vacant for the element that where yet to be discovered . He even predicted the properties of such element and of sum of their compound fairly accurately . in some cases, he event divorced the order of some elements , if it better matched their properties .proceeding in this manner he could arrange all the known element in his periodic table .
when more element were discovered this periodic table was modified and updated to include them . One more group zero group had to be added when noble gas were discovered .
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