Which of the following is a Dobereiner’s Triads ? a. Li, Na, K b. Li, Sr, I c. Li, Ca, Cl d. Kr, Br, I …
The Correct Answer and Explanation is:
The correct answer is a. Li, Na, K.
Explanation:
Dobereiner’s Triads refer to a concept in early chemistry, proposed by Johann Wolfgang Döbereiner in the early 19th century. Döbereiner noticed that certain groups of three elements had a particular pattern in their atomic weights. Specifically, he observed that the atomic weight of the middle element in a triad was approximately the average of the atomic weights of the other two elements.
In the case of Li, Na, K, these elements form a triad, as the atomic weights of lithium (Li), sodium (Na), and potassium (K) follow the pattern described by Döbereiner:
- Li (Lithium): Atomic weight = 6.94
- Na (Sodium): Atomic weight = 22.99
- K (Potassium): Atomic weight = 39.10
The atomic weight of sodium is close to the average of lithium and potassium: Average of Li and K=6.94+39.102=23.02\text{Average of Li and K} = \frac{6.94 + 39.10}{2} = 23.02Average of Li and K=26.94+39.10=23.02
This shows that the middle element, sodium, fits the pattern of being the average of the first and third elements.
The other options do not follow the same pattern:
- b. Li, Sr, I: There is no consistent relationship between the atomic weights of these elements.
- c. Li, Ca, Cl: These elements do not form a triad according to Döbereiner’s rules.
- d. Kr, Br, I: Similarly, these elements don’t fit the triad concept.
Thus, Li, Na, K is the correct example of a Dobereiner’s Triad.
