Question

(46) (a) State the merits of Mendeleev's classification of elements.
(b) Describe two anomalies of Mendeleev's periodic classification of elements.


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Answer 1

(a) The merits of Mendeleev's classification of elements:

(i) Mendeleev's periodic law predicted the existence of certain elements such as gallium, scandium and germanium, which

were not discovered at that time.

(ii) Mendeleev's periodic table could also predict the properties of various elements based on their position in the periodic

table.

(iii) Mendeleev's periodic table could place group 18 elements, called Noble gases in the periodic table, when they were

discovered.

(b) Anomalies of Mendeleev's periodic classification of elements:

(i) Mendeleev's periodic classification of elements could not explain the position of isotopes in the periodic table: Since,  

isotopes of the same metal have similar chemical properties but different in their atomic masses.

So, the isotopes of the same element should be given different place in periodic table as Mendeleev's periodic table was

arranged in increasing order of their atomic masses.

However, isotopes were not given separate place in his periodic table.

(ii) Mendeleev's periodic classification of elements could not assign a proper place for the element, hydrogen.

Since, hydrogen resembled both alkali metals and halogens in some of the properties.

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Answer 2

Answer:

1. mendeleev periodic law predicted the existence sof certain element such as scandium gallium and germanium.

2. mendeleev periodic table could place group 18 elements called noble gases in the periodic table when they were discovered.

3.Anomalies of mendeleev periodic classification of element show the isotopes of the same element should be given different place in periodic table as mendeleev periodic table was arranged in increasing order of their atomic masses .however isotopes were not given separate place in his periodic table.