Question

Choose two more groups of elements in the periodic table that Döbereiner could have identified as 'triads’

Answer 1

Answer:

The examples of Döbereiner Triad are :

Lithium , Sodium and Potassium

Calcium , Strontium and Barium

Chlorine , bromine and iodine

Sulfur , Selenium and Tellurium

Explanation:

Döbereiner Triad : He arranged the element in increasing order of their atomic weight and found that the weight of the middle element is equal to the mean(=average) of the atomic weight of the first and third element .

The example of Döbereiner triad are :

Lithium , Sodium and Potassium

Calcium , Strontium and Barium

Chlorine , bromine and iodine

Sulfur , Selenium and Tellurium

Now, let's know how Döbereiner  actually arrived at the result:

1.Lithium , Sodium and Potassium

According to his rule , The mass of Sodium(Middle element) can be calculated :

Mass of Sodium=

$\frac{mass\ of\ Lithium+mass\ of\  Potassium}{2}$

Let's check whether this follow , the Döbereiner triad or not:

mass of Li = 6.94

Mass of Sodium = 23.03

mass of Potassium = 39.10

So according to Döbereiner , the mass of Sodium should be:

$\frac{6.94+39.10}{2}$

= 22.99

Actual mass = 23 .02

Hence , it is very close to the result. Thus Döbereiner triad is followed by these element.

Similarly for ,

Chlorine , bromine and iodine

mass of Cl = 35.47

mass of iodine = 126.47

So mass of bromine should be ,

$\frac{35.47+126.47}{2}$

= 70.38

The actual mass of bromine was : 80.47 (almost equal to calculated)

But later it was found that not all elements follow this rule. So this theory was later modified by other scientists.