Question

Identify the third element of the following Döbereiner's triads.

• A. Potassium
• B. Barium
• C. Iodine

Answer 1

According to Dobereiner, when the three elements in a triad are written in the increasing order of atomic masses, the atomic mass of the middle element is roughly the average of the atomic masses of the other two elements.

Calculation:
a) Atomic masses of Lithium = 7, Sodium = 23 and Potassium = 39
$\Rightarrow \frac{(7+39)}{2}=23$

b) Atomic masses of Calcium = 40, Strontium = 89 and Barium = 137
$\Rightarrow \frac{(40+137)}{2}=88.5$

c) Atomic masses of Chlorine = 35.5, Bromine = 80.5 and Iodine = 126
$\Rightarrow \frac{(35.5+126)}{2}=80.75$