Question

2. In Dobereiner's triads Li, Na, K, the atomic masses of
Lithium and Potassium are 6.9 and 39.1 respectively, then
what will be the atomic mass of sodium.​

Answer 1

Answer:

23

Explanation:

$6.9 + 39.1 =46 \\ \\ 46 \div 2 = 23$

According to Dobernier the mean of the mass of 1 and 3 element is equal to 2 element's mass

Answer 2

SOLUTION:

Dobreiner classified that atomic mass of the middle element is roughly the average of the other two elements.

That means, in the triad of Li, Na and K, atomic mass of Sodium (Na) will be average of Lithium and Potassium.

Given, Atomic mass of Lithium (Li) = 6.9 u

Atomic mass of Potassium (K) = 39.1 u

∴ Atomic Mass of (Na) = Average of (Li + K)

= (6.9 + 39.1)/2

= 46/2

= 23

∴ Atomic Mass of Sodium is 23 u ✅

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Additional Information

• The first ever classification of elements was done by Johann Wolfgang Dobreiner in the 18th century.

• Dobreiner's triads include (Li, Na, K) , (Ca, Sr, Ba) and (Cl, Br, I).

• Elements in a triad had similar chemical and physical properties.

• Dobreiner's triads had a lot of limitations, and was not appropriate in studying modern elements. He could only find three triads like these from the known elements.