Dobereiner's triads were groups of elements with similar properties that were identified by the German chemist Johann Wolfgang Dobereiner. He observed that groups of three elements (triads) could be formed in which all the elements shared similar physical and chemical properties.Dobereiner's Triad
He found that the atomic mass of the middle element was approximately equal to the arithmetic mean (average) of the atomic masses of the other two elements of that triad when they are arranged in their increasing order of atomic mass, e.g., Li, Na, K. The atomic mass of Li is 9 and K is 39.
[tex]\:\:\:\:\:\:\:\:\:\:[/tex] Acoording to Doberenier's law of traids, 'If the elements having similar chemical properties are arranged in sets of three elements in increasing order of their atomic weights, the atomic weights of the middle element was nearly the mean of the atomic weight of the other two elements.
Let's take an Example
[tex]\:\:\:\:\:\:\:\:\:\:[/tex]Here, we take three elements A, B, and C having increasing atomic weights respectively,
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex][tex]\color{vlack}\boxed{\dfrac{A + C }{ 2} = B }[/tex]
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex] Doberenier could find only 3 traids. [ 9 elements ] .
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex] Also , law of traids was rejected as some traids have nearly same atomic masses . Also all elements known at the time could not be classified in traids.
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Answer:
Dobereiner's triads were groups of elements with similar properties that were identified by the German chemist Johann Wolfgang Dobereiner. He observed that groups of three elements (triads) could be formed in which all the elements shared similar physical and chemical properties.Dobereiner's Triad
He found that the atomic mass of the middle element was approximately equal to the arithmetic mean (average) of the atomic masses of the other two elements of that triad when they are arranged in their increasing order of atomic mass, e.g., Li, Na, K. The atomic mass of Li is 9 and K is 39.
Verified answer
[tex]\:\:\:\:\:\:\:\:\:\:[/tex] Acoording to Doberenier's law of traids, 'If the elements having similar chemical properties are arranged in sets of three elements in increasing order of their atomic weights, the atomic weights of the middle element was nearly the mean of the atomic weight of the other two elements.
Let's take an Example
[tex]\:\:\:\:\:\:\:\:\:\:[/tex]Here, we take three elements A, B, and C having increasing atomic weights respectively,
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex][tex]\color{vlack}\boxed{\dfrac{A + C }{ 2} = B }[/tex]
[tex]\large\underline\color{green}{\sf{Achievements\: : - }}[/tex]
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex]It recognised a relationship between properties of elements and their atomic masses
[tex]\large\underline\color{green}{\sf{Limitations\: : - }}[/tex]
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex] Doberenier could find only 3 traids. [ 9 elements ] .
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex] Also , law of traids was rejected as some traids have nearly same atomic masses . Also all elements known at the time could not be classified in traids.
Set - 1
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex] \begin{array}{r | l } Element & Atomic \:mass \\ \cline{1-2} Calcium& 40 \\ \cline{1-2} Strontium & 87.5 \\ \cline{1-2} Barium & 13.7 \end{array}[/tex]
Here, Average of the atomic masses of Calcium and Barium
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex] [tex]\color{black}\boxed{\dfrac{\cancel40 +\cancel 137}{\cancel2} = 88.5}[/tex]
Atomic mass of Strontium = [tex]\color {red}{87.5}[/tex]
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Set - 2
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex] \begin{array}{r | l } Element & Atomic \:mass \\ \cline{1-2} Lithium& 7 \\ \cline{1-2} Sodium& 23\\ \cline{1-2} Potassium & 39 \end{array}[/tex]
Here, Average of the atomic masses Lithium and Potassium
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex] [tex]\color{black}\boxed{\dfrac{\cancel 7 +\cancel 39}{\cancel2} = 23}[/tex]
Atomic mass of Potassium= [tex]\color {red}{23}[/tex]
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Set - 3
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex] \begin{array}{r | l } Element & Atomic \:mass \\ \cline{1-2} Chlorine& 35.5 \\ \cline{1-2} Bromine& 80\\ \cline{1-2} Iodine & 27 \end{array}[/tex]
Here, Average of the atomic masses Chlorine and Iodine
[tex]\:\:\:\:\:\:\:\:\:\:[/tex][tex]\hookrightarrow[/tex] [tex]\color{black}\boxed{\dfrac{\cancel 35.5 +\cancel 27}{\cancel2} = 81.2}[/tex]
Atomic mass of Potassium= [tex]\color {red}{80}[/tex]