Question

State Dobereiner's Triads giving one example.

Answer 1

Hint: Dobereiner's Triads help in grouping the elements based on a distinguishing property. Identify the property for grouping. With this you can make these triads which will serve as an example to support the theory.

Complete step by step answer:
We know that in the course of the 17th and 18th century, many new elements were discovered Due to this the broad classification of elements as metals and nonmetals became inefficient and obsolete.
Several experiments were carried out in order to identify elements having similar physical and chemical properties and hence can be grouped together.
Dobereiner stated in the law of triads that the arithmetic mean of the atomic masses of the first and third element in the triad should be equal to or almost equal to the atomic mass of the second element present in the triad. He also suggested that this law could be extended for other quantifiable properties of elements for e.g. density.
The first of these triads were identified in 1817 and consisted of the alkali earth metals, calcium, strontium and barium.

There more triads were identified by the end of 1829. The three triads are mentioned below:
Triad 2:
- Lithium
- Sodium
- Potassium

Triad 3:
- Chlorine
- Bromine
- Iodine

Triad 4:
- Sulfur
- Selenium
- Tellurium

Note: Although Dobereiner was successful in identifying the common properties between elements, it had some shortcomings as well. Some are mentioned below:
- The identification of new elements made his law of triads incapable and obsolete
 -Newly discovered elements had no place in the triads
- Only a total of 5 triads were able to be formed
- Some known elements at that moment couldn’t be grouped with the existing triads