Question

The three elements A, B, and C with similar properties have atomic masses X, Y, and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called? Give one example of such a set of elements.

Answer 1

1. Triads are a particular type of arrangement of components. Johann Wolfgang Dobereiner, a German scientist, discovered groupings of elements having related characteristics and named them Dobereiner's triads.
2. The arithmetic mean of the atomic masses of the first and third elements in a triad would be about equal to the atomic mass of the second element in that triad, according to Dobereiner's law of triads. Additionally, he proposed that this law be expanded to include additional components' quantitative attributes, such as density.

Example:

1. A triad is formed of Lithium, Sodium and Potassium. Their respective atomic masses are $6.9\mathrm{g},23.0g$ and $39.0$g.
2. The atomic mass of Na is about equivalent to the average masses of $Li$ and $K$.