Medium
Explain the "Law of Triads" with examples.
(N/A) The German chemist,Johann Dobereiner,was the first to consider the idea of trends among the properties of elements.
He noted a similarity among the physical and chemical properties of groups of three elements,which he called "Triads".
"Law of Triads":
- "The atomic weight of the middle element of each of the Triads was approximately the arithmetic mean of the atomic weights of the other two elements."
Conclusion: The atomic weight of the middle element is approximately equal to the average of the atomic weights of the first and third elements.
He noted a similarity among the physical and chemical properties of groups of three elements,which he called "Triads".
"Law of Triads":
- "The atomic weight of the middle element of each of the Triads was approximately the arithmetic mean of the atomic weights of the other two elements."
| Triad Number | Elements and Atomic Weights | Average of $1^{st}$ and $3^{rd}$ element |
| $(1)$ | $Li(7), Na(23), K(39)$ | $(7+39) / 2 = 23$ |
| $(2)$ | $Ca(40), Sr(88), Ba(137)$ | $(40+137) / 2 = 88.5$ |
| $(3)$ | $Cl(35.5), Br(80), I(127)$ | $(35.5+127) / 2 = 81.25$ |
Conclusion: The atomic weight of the middle element is approximately equal to the average of the atomic weights of the first and third elements.
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Write the drawbacks in Mendeleev's periodic table that led to its modification.
Given below are two statements :
Statement $(I):$ According to the Law of Octaves,the elements were arranged in the increasing order of their atomic number.
Statement $(II) :$ Meyer observed a periodically repeated pattern upon plotting physical properties of certain elements against their respective atomic numbers.
In the light of the above statements,choose the correct answer from the options given below :
Statement $(I):$ According to the Law of Octaves,the elements were arranged in the increasing order of their atomic number.
Statement $(II) :$ Meyer observed a periodically repeated pattern upon plotting physical properties of certain elements against their respective atomic numbers.
In the light of the above statements,choose the correct answer from the options given below :
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Easy
View SolutionWrite a note on the genesis of the periodic table.
Given below are the atomic masses of the elements:
Element $Li$ $Na$ $Cl$ $K$ $Ca$ $Br$ $Sr$ $I$ $Ba$ Atomic Mass $(g \cdot mol^{-1})$ $7$ $23$ $35.5$ $39$ $40$ $80$ $88$ $127$ $137$
Which of the following does not form a $Dobereiner's$ triad?
| Element | $Li$ | $Na$ | $Cl$ | $K$ | $Ca$ | $Br$ | $Sr$ | $I$ | $Ba$ |
|---|---|---|---|---|---|---|---|---|---|
| Atomic Mass $(g \cdot mol^{-1})$ | $7$ | $23$ | $35.5$ | $39$ | $40$ | $80$ | $88$ | $127$ | $137$ |
Which of the following does not form a $Dobereiner's$ triad?
MediumKCET 2025
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