Chemistry
Grade-9
Easy
Question
Select the correct order we need to put sodium, potassium, lithium, for Dobereiner's Law of Triads?
- Lithium, sodium, potassium
- Sodium, lithium, potassium
- Potassium, lithium, sodium
- Sodium, potassium, lithium
Hint:
Dobereiner’s triads were groups of three elements each that could be formed in which all the elements shared similar physical and chemical properties. For this, the arithmetic mean of the atomic masses of the first and third elements in a triad would be approximately equal to the atomic mass of the second element in that triad.
The correct answer is: Lithium, sodium, potassium
Atomic Masses of Lithium, Sodium and Potassium are 6.94, 22.99 and 39.1 respectively. As is evident, the arithmetic mean of the masses of potassium and lithium corresponds to 23.02, which is almost equal to the atomic mass of sodium. Hence, the correct sequence is Lithium, Sodium, and Potassium.
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