Dobereiner’s Triads

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  • Dobereiner’s Triads
  • Limitations of Dobereiner’s Triads

DOBEREINERS TRIADS:-

In 1817, Johann Wolfgang Döbereiner, a German chemist, tried to arrange the elements with similar properties into groups. He identified some groups having three elements each. So he called these groups ‘triads’.

When the three elements in a triad were written in the order of increasing atomic masses, the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

For example:-

lithium (Li)

6.9

sodium (Na)

23.0

potassium (K)

39.0

The average atomic mass of the first and the last element is 22.95, which is almost equal to the middle element.

Limitation:-

Döbereiner could identify only three triads from the elements known at that time. Hence, this classification system into triads was not found to be helpful.

These were the only triads recognised from the elements known at that time.

(i) Li, Na, K

(ii) Ca, Sr, Ba

(iii) Cl, Br, I

 

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