Question

write a short note on Dobereiners Triads

Answer 1

In the history of the periodic table, Döbereiner's triads were an early attempt to sort the elements into some logical order by their physical properties. In 1817, a letter reported Johann Wolfgang Döbereiner's observations of the alkaline earths; namely, that strontium had properties that were intermediate to those of calcium and barium.[1] By 1829, Döbereiner had found other groups of three elements (hence "triads") whose physical properties were similarly related.[2] He also noted that some quantifiable properties of elements (e.g. atomic weight and density) in a triad followed a trend whereby the value of the middle element in the triad would be exactly or nearly predicted by taking the arithmetic mean of values for that property of the other two elements.

Predicted vs actual atomic mass of the central atom of each triad
Triad name[2] Elements and atomic masses[2][3]
Element 1
Mass Element 2
Mean of 1 and 3
Actual mass Element 3
Mass
Alkali-forming elements Lithium
6.94 Sodium
23.02
22.99 Potassium
39.10
Alkaline-earth-forming elements
[atomic masses verification needed] Calcium
40.1 Strontium
88.7
87.6 Barium
137.3
Salt-forming elements Chlorine
35.470 Bromine
80.470
78.383 Iodine
126.470
Acid-forming elements Sulfur
32.239 Selenium
80.741
79.263 Tellurium
129.243
-
[atomic masses verification needed] Iron
55.8 Cobalt
57.3
58.9 Nickel
58.7
References Edit

Answer 2

dobereiner was a scientist that made 3 traids of 30 elements that were known at that time .