Question

state two criteria used by Mendeleev to classify the elements in his periodic table

Answer 1

A) Mendeleev used increase in atomic mass and formulae of hydrides and oxides as the 2 main criteria. b) Properties of elements are a periodic function of their atomic masses. c) Hydrogen exists as diatomic molecules, similar to those of Group 17. However, it also has 1 valence electron, like Group 1 elements.

Answer 2

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 .  This states that :-

Properties of elements are the periodic function of their atomic masses .  


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