Which scientist arranged some elements in groups of three, in which the atomic mass of the middle element was roughly the average of the other two, as in lithium, sodium and potassium?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Johann Wolfgang Döbereiner
The German chemist Döbereiner grouped similar elements in threes, called triads. In the triad lithium (7 u), sodium (23 u) and potassium (39 u), the middle atomic mass is about the average of the other two: \((7+39)\div2=23\).