Question

explain dobereiner's law of triad's with an example​

Answer 1

Answer:

According to Dobereiner, all elements occurred in groups of three, when arranged in increasing order of atomic masses. He referred to these groups as triads. In a traid the elements had similar chemical properties.  Traids of the Dobereiners classification: Traid1:

ElementAtomic massLithium (Li)7Sodium (Na)23Potassium (K)39

Traid2:

ElementAtomic massChlorine (Cl)35.5Bromine (Br)80Iodine (I)127

Traid3:

ElementAtomic massCalcium (Ca)40Strontium (Sr)88Barium (Ba)137

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.   Example:In the triad of lithium, sodium and potassium. The atomic mass of lithium is 7 and  the atomic mass of potassium is 39. The average of masses of lithium and potassium gives atomic mass of sodium 23.  Drawbacks: All the known elements could not be arranged in the form of triads. This law did not hold good for elements with very low or very high atomic mass.  Example: The arithmetic mean of the atomic masses of fluorine 19 and bromine 80, which comes to 49.5, varies significantly from the atomic mass of chlorine, which is 35.5.

Answer 2

Answer:

When elements are arranged in oder of their atomic masses then the average of first and third element atomic masses is equal to the atomic mass of second element.

Explanation:

For example- In alkaline earth metals group the first element is beryllium, the middle element is magnesium and the third element is calcium, so acc. To the Debereiner’s triad the arithmetic mean of the atomic masses beryllium and calcium is equal to the atomic mass of magnesium.