Dobereiner's Triads : Law Theory Merits Demerits
Definition of Dobereiner's theory law in English and Hindi
When elements are arranged in the order of increasing atomic masses, groups of 3 elements (known as triads), having similar properties are obtained. The atomic mass of the middle element of the triad being equal to the Arithmetic mean of the atomic masses of the other two elements.
वुल्फगांग डॉबेराइनर ने बताया कि त्रिक के तीनों तत्वों को उनके परमाणु द्रव्यमान (Atomic mass) के आरोही क्रम (increasing order) में रखने पर बीच वाले तत्व का परमाणु द्रव्यमान (Atomic mass), अन्य दो तत्वों के परमाणु द्रव्यमान (Atomic mass) का लगभग औसत होता है।
यथा: लीथियम (Li), सोडियम (Na) तथा पोटैशियम (K), जिनका परमाणु भार (Atomic mass) क्रमश: 7.0, 23.0, तथा 39.0 है। इनमें बीच वाले तत्व सोडियम (Na) का परमाणु भार (Atomic mass) अन्य दो तत्वों लीथियम (Li) तथा पोटैशियम (K) के परमाणु द्रव्यमान (Atomic mass) का औसत है।
In earlier time, the elements were Classified on the basis of their properties. The elements which have similar properties where put in one group and this group is called a family. In 1829, are German chemist Dobereiner's found that certain elements have similar properties and he put them together in a group of three. This groups of three elements are called triads.
Example of triads:
1. The alkali metal group: elements like Lithium, Sodium, Potassium have similar chemical properties and form a triad.
(i) all these elements are metals
(ii) all of them react with water to form alkalis and hydrogen.
(iii) all of them have a valency of one.
The atomic mass of Lithium is 7, ant the element potassium has atomic mass 39.
So, Arithmetic mean of atomic masses of Lithium and sodium= (7+39)/2=23
Actual atomic mass of sodium is 23.
From this calculation we find that automatic mean of the atomic masses of Lithium and potassium is 23 which is equal to the actual atomic mass of the middle element of the triad, sodium. Hence Lithium, Sodium, Potassium are triads elements.
The alkaline earth metal group: the elements like calcium, strontium, barium also forms triad. Because
(i) all these elements are metals
(ii) the oxides of all of them are alkaline in nature
(iii) all these elements have a valency of 2.
Now atomic mass of calcium is 40 and atomic mass of Barium is 137.
Show the athletic mean of atomic masses of calcium and barium= (40+137)/2= 88.5.
The actual atomic mass of Strontium is 88.
Does the atomic mass of the middle element of this (Strontium) is approximately equal to the Arithmetic mean of the atomic masses of the first and third elements that is calcium and barium.
Hence calcium Strontium and barium forms triads.
The Halogen group:
Elements in halogen groups like chlorine, bromine, Iodine forms triads. Because
(i) all these elements are non metals
(ii) all these elements react with water to form acids
(iii) all these elements have valency 1.
Know the atomic mass of chlorine is 35.5 and atomic mass of iodine is 127.
So, Arithmetic mean of atomic masses of chlorine and Iodine=(35.5+127)/2=81.2
The actual atomic mass of bromine is 80.
Thus the atomic mass of the middle element of this triad (beomine) is approximately equal to the Arithmetic mean of the atomic masses of the first and third elements of the triad that is chlorine and Iodine.
Hence chlorine, bromine, Iodine forms triads.
Merits of Dobereiner 's triads: Advantage of Dobereiner's law that it made a look at elements in terms of groups of elements with similar chemical and physical properties.
Dobereiner's law of triads limitation or demerits or disadvantages of this classifications:
This law failed to arrange all the elements in the form of triads of elements having similar chemical properties. Dobereiner's Could identify only three triads from the elements known at that time.
What were the limitations of Dobereiner's classification?
All the elements discovered at that time could not be classified into triads, only a limited number of elements could be arrange d insearch triads.
As for example, the three elements nitrogen, phosphorus, arsenic have similar properties. Therefore they should be regarded to form a triad. Howevee, the actual mass of the middle element that is phosphorus has atomic mass free 31.04 which is March lower than the average (44.454) atomic masses of Nitrogen and arsenic.
Did Dobereiner's triads also exist in the columns of newlands octaves? Compare and find out.
Answer: yes, Dobereiner's triads also exist in the columns of newlands octaves. As for example Lithium, Sodium, Potassium constitute a Dobereiner's triads. Now if we consider Lithium as the first element then the earth element from it, is Sodium and if we consider sodium as the first element then the 8th element from it is Potassium.
When elements are arranged in the order of increasing atomic masses, groups of 3 elements (known as triads), having similar properties are obtained. The atomic mass of the middle element of the triad being equal to the Arithmetic mean of the atomic masses of the other two elements.
वुल्फगांग डॉबेराइनर ने बताया कि त्रिक के तीनों तत्वों को उनके परमाणु द्रव्यमान (Atomic mass) के आरोही क्रम (increasing order) में रखने पर बीच वाले तत्व का परमाणु द्रव्यमान (Atomic mass), अन्य दो तत्वों के परमाणु द्रव्यमान (Atomic mass) का लगभग औसत होता है।
यथा: लीथियम (Li), सोडियम (Na) तथा पोटैशियम (K), जिनका परमाणु भार (Atomic mass) क्रमश: 7.0, 23.0, तथा 39.0 है। इनमें बीच वाले तत्व सोडियम (Na) का परमाणु भार (Atomic mass) अन्य दो तत्वों लीथियम (Li) तथा पोटैशियम (K) के परमाणु द्रव्यमान (Atomic mass) का औसत है।
In earlier time, the elements were Classified on the basis of their properties. The elements which have similar properties where put in one group and this group is called a family. In 1829, are German chemist Dobereiner's found that certain elements have similar properties and he put them together in a group of three. This groups of three elements are called triads.
Example of triads:
1. The alkali metal group: elements like Lithium, Sodium, Potassium have similar chemical properties and form a triad.
(i) all these elements are metals
(ii) all of them react with water to form alkalis and hydrogen.
(iii) all of them have a valency of one.
The atomic mass of Lithium is 7, ant the element potassium has atomic mass 39.
So, Arithmetic mean of atomic masses of Lithium and sodium= (7+39)/2=23
Actual atomic mass of sodium is 23.
From this calculation we find that automatic mean of the atomic masses of Lithium and potassium is 23 which is equal to the actual atomic mass of the middle element of the triad, sodium. Hence Lithium, Sodium, Potassium are triads elements.
The alkaline earth metal group: the elements like calcium, strontium, barium also forms triad. Because
(i) all these elements are metals
(ii) the oxides of all of them are alkaline in nature
(iii) all these elements have a valency of 2.
Now atomic mass of calcium is 40 and atomic mass of Barium is 137.
Show the athletic mean of atomic masses of calcium and barium= (40+137)/2= 88.5.
The actual atomic mass of Strontium is 88.
Does the atomic mass of the middle element of this (Strontium) is approximately equal to the Arithmetic mean of the atomic masses of the first and third elements that is calcium and barium.
Hence calcium Strontium and barium forms triads.
The Halogen group:
Elements in halogen groups like chlorine, bromine, Iodine forms triads. Because
(i) all these elements are non metals
(ii) all these elements react with water to form acids
(iii) all these elements have valency 1.
Know the atomic mass of chlorine is 35.5 and atomic mass of iodine is 127.
So, Arithmetic mean of atomic masses of chlorine and Iodine=(35.5+127)/2=81.2
The actual atomic mass of bromine is 80.
Thus the atomic mass of the middle element of this triad (beomine) is approximately equal to the Arithmetic mean of the atomic masses of the first and third elements of the triad that is chlorine and Iodine.
Hence chlorine, bromine, Iodine forms triads.
Merits of Dobereiner 's triads: Advantage of Dobereiner's law that it made a look at elements in terms of groups of elements with similar chemical and physical properties.
Dobereiner's law of triads limitation or demerits or disadvantages of this classifications:
This law failed to arrange all the elements in the form of triads of elements having similar chemical properties. Dobereiner's Could identify only three triads from the elements known at that time.
What were the limitations of Dobereiner's classification?
All the elements discovered at that time could not be classified into triads, only a limited number of elements could be arrange d insearch triads.
As for example, the three elements nitrogen, phosphorus, arsenic have similar properties. Therefore they should be regarded to form a triad. Howevee, the actual mass of the middle element that is phosphorus has atomic mass free 31.04 which is March lower than the average (44.454) atomic masses of Nitrogen and arsenic.
Did Dobereiner's triads also exist in the columns of newlands octaves? Compare and find out.
Answer: yes, Dobereiner's triads also exist in the columns of newlands octaves. As for example Lithium, Sodium, Potassium constitute a Dobereiner's triads. Now if we consider Lithium as the first element then the earth element from it, is Sodium and if we consider sodium as the first element then the 8th element from it is Potassium.
