Question

write one disadvantage of mendeleev's periodic table​

Answer 1

Answer:

Mendeleev’s table was an amalgam of the compilations that had been made in the previous ninety years. All of them, and Mendeleev’s, were based on ordering the elements by atomic weight. Mendeleev incorporated the most recent finding and measurements of those atomic weights, and presented the data in a novel arrangement. In this way, he could foresee the presence of new elements that should be found in certain positions in the table, positions that were currently empty. He even made predictions about their chemical properties, which turned out to be true when the new elements were found..

Despite all these things to its credit, there remained several anomalies in the table that were not consistent with experimental observations. Elements seemed to be in the wrong column, based on their properties ; some pairs of adjacent elements were obviously ordered wrongly, and there were other problems as well.

All these difficulties were resolved when Moseley ordered the elements by atomic number rather than atomic weight. He had discovered an X-Ray Fluorescence analytical spectroscopic technique that would conclusively identify the atomic number of an element, not matter whether the sample was a known element or not.

In Moseley’s new ordering were 92 atomic number positions for all the elements. At that time, Hydrogen was # 1 and Uranium was # 92. This ordering pinpointed the atomic numbers for which no element was known. The misordering of the elements under the old atomic weight system was put right, and it became easier to identify an element — even a new one that no one had discovered before — using Moseley’s X-Ray Fluorescence.

So it turned out that those so called “drawbacks” in the old periodic table were the best thing that could have happened to it.

Answer 2

Explanation:

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.