Question

Write short notes
a. Mendeleev's periodic law.
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Answer 1

Answer:

Mendeleev's Periodic Law states that the physical and the chemical properties of the elements are a periodic function of their atomic masses. Mendeleev arranged the elements known at that time in order of increasing atomic masses and this arrangement was called periodic table

The elements having similar chemical properties form oxides and hydrides having similar formulae. Mendeleev used these properties for creating his periodic table.

Limitations of Mendeleevs classification of elements:

(i) The position of isotopes could not be explained.

(ii) Wrong order of atomic masses of some elements could not be explained.

(iii) A correct position could not be assigned to Hydrogen in the periodic table.

(d) Silicon and Germanium.

(e) Noble gases were missing from Mendeleev's original periodic table.

Answer 2

Answer:

Mendeleev’s periodic law.

• According to Mendeleev’s Periodic Law, “Physical and chemical properties of elements are periodic function of their atomic masses”.

• Mendeleev classified elements according to their atomic masses and arranged these elements in increasing order of  their atomic masses.

• Mendeleev classified periodic table into horizontal rows and vertical coloumns. The horizontal rows are called as periods and vertical columns are called groups. Mendeleev’s Periodic Table contains seven horizontal rows and nine vertical columns.

• The elements with similar properties comes into same group.

• Mendeleev also left gaps in his periodic table for undiscovered elements like aluminum, silicon and Boron in his periodic table and named them Eka-Aluminium, Eka-silicon and Eka-Boron.

• Mendeleev not only predicted the existence of Eka-Aluminium, Eka-silicon and Eka-Boron but also described the general physical properties of these elements.

• These elements discovered later and named as Gallium, Germanium and Scandium.

• Mendeleev's periodic table could predict the properties of several elements on the basis of their position in the periodic table.

• Mendeleev's periodic table could accomodate noble gases when they were discovered.

Demerits of Mendleev's periodic table:

• The position of isotopes could not explained.

• Wrong order of atomic masses of some elements could not be explained.

• Position of Hydrogen could not be assigned in a periodic table.

Explanation: