Question

Is Fe, Co, Ni the Dobereiner triad?

Answer 1

Hint: In 1829, a German chemist, Johann Dobereiner, placed various groups of three elements into groups called triad. In order to answer this question you need to recall Dobereiner’s law of triads.

Complete step by step answer:

• Basically, dobereiner observed that certain elements observed certain elements which had similar chemical properties, could be grouped together.
• When these particular similar elements were arranged in increasing order of their atomic masses, they generally occurred in groups of three. These groups were called triads.
• He noticed that the atomic mass of the middle element of the middle element of the arithmetic mean of the other two elements of the triad. This was known as Dobereiner’s triad.
• Therefore, this law states that when elements are placed in ascending order of atomic masses, a group of three elements having similar properties are obtained. The atomic mass of the middle element of the triad is equal to the mean of the atomic masses of the other two elements of the triad.

Example of Dobereiner’s triad:
The elements lithium, sodium and potassium form a dobereiner’s triad. Lithium being the first element of this triad, sodium is the middle element whereas potassium is the third element of the triad.
Arithmetic mean of Li and K = $\dfrac { 7+39 }{ 2 }$ =23
It can be seen that arithmetic mean of the atomic masses of Li and K = atomic mass on Na.

Considering the question as the atomic weight of the middle element is not the same as an average of the weight of the other two elements. Therefore, Fe, Co, Ni is not a Doberiner triad.

Note : Drawbacks of this law, all the elements could not be arranged in the form of triads. This law did not hold good for elements with very low or very high atomic mass.