Student Projects/Doberenier triad

Scientists have made several attempts to classify elements that were known by their time. Classifying elements was found important so that it would facilitate choosing the elements for further applications when required.

Dobereiner was the first person to make an attempt to classify elements,

1) He found that in a triad the atomic mass of middle element was roughly the arithmetic mean of the atomic mass of the 1st and 3rd element. 
dobereiner triads
Ca 40.1
Sr 87.5
Ba 137.5

2) The attempt to classify elements was appreciated but there were limitations

(i) when he classified,only 56 elements were known at that time and he could make triads only for about 9 elements

(ii)all the elements couldn't be classified as only Dobereiner's triads was applicable only till Z=20 elements.