Question

State Dobereiner’s Law of Triads with suitable examples.

Answer 1

Dobereiner’s Law of Triads: “When elements are arranged in order of increasing atomic masses, groups of three elements (known as triads), having similar chemical properties are obtained. The atomic mass of the middle element of the triad being equal to the arithmetic mean of the atomic masses of the other two elements.”
Examples:
Similarity in properties

Element	Lithium	Sodium	Potassium
At. weight	7.0	23.0	39.0

1. All of them are metals. Average wt. of sodium 7 + 39/2 = 46/2 = 23
2. All have valency 1.
3. They react with water form alkalis and hydrogen gas.

Halogen Group:

\[\ce{Cl}\]	\[\ce{Br}\]	\[\ce{I}\]
35.5	80	127

1. All of them are non-metals
2. All have valency one (1).
3. Each reacts with water to form acid.