Question

Definition of Dobereiner's triads. ​

Answer 1

Dobereiner's law of triads states that, the atomic mass of the middle element of a triad is the arithmetic mean of the atomic masses of the other two elements.

Answer 2

Hey!

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Dobereiner's law of triad states -:

When elements are placed in an ascending order of atomic masses, group of three elements having similar properties are obtained. The atomic mass of middle element of the triad is approximately equal to the mean of atomic masses of other two events in the triad.


First Triad Discovered -:

Lithium ____ Li _____ 7
Sodium ____ Na ____ 23
Potassium ____ K _____ 39

Arithmetic mean of Li, K = 39 + 7 / 2 = 23
Atomic mass of Na = 23




Calcium ______ Ca _____ 40
Strontium ______ Sr ______ 87.6
Barium ______ Ba ______ 137

Mean of Ca and Ba = 88.5 (approx)
Atomic mass of Sr = 87.6



Chlorine ______ Cl ____ 35.5
Bromine ______ Br ____ 80
Iodine _______ I _____ 127

The mean will be near about 80.


DISADVANTAGES of Dobereiner's Law of Triads -:

• All the then known elements could not be categorised into group of Triads.
For example : F , Cl , Br

• Law was not applicable for very low mass or very high mass elements

• He could only make 3 Triads.

The only achievement was that he was the first person to make attempts on classifying the elements.

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Hope it helps!