Question

If the atomic weight of chlorine is 35.5 and the atomic weight of iodine is 126.5, what is the expected atomic weight of bromine? Explain logically.

Answer 1

1. Dobereiner's triads: Chlorine, Bromine, and Iodine form a Dobereiner's triad (Cl, Br, I). It states that the atomic mass of the middle element is approximately the arithmetic mean of the atomic mass of the other two elements.

2. Calculate the atomic weight of Bromine:

$Atomicmassofmiddleelement=\frac{\mathrm{Sum}\mathrm{of}\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{other}\mathrm{two}\mathrm{elements}}{2}$

$$\begin{gathered} AtomicmassofBromine=\frac{\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{Chlorine}+\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{Iodine}}{2} \\ =\frac{35.5+126.5}{2} \\ =\frac{162}{2}=81 \end{gathered}$$

Thus, the expected atomic weight of Bromine is 81.