Question

Consider a Dobereiner's triad with elements X, Y, and Z. The sum of atomic weights of extreme elements X and Z is 46, and the difference in atomic weights of Z and Y is two times the atomic number of oxygen. Identify the X, Y, and Z.

Answer 1

Doberenier's law of Triads-

When elements are arranged in the order of increasing atomic masses, groups of three elements (known as triads), having similar chemical properties are obtained. The atomic mass of the middle element of the triad is equal to the arithmetic mean of the atomic masses of the other two elements.

• According to the question, $\mathrm{X}+\mathrm{Z}=46$ -------- (1)
• $Z-Y=2\left(8\right)=16$ ---------(2)
• Since, X, Y, and Z follow Dobereiner's law of triads.
• Hence, $\frac{\mathrm{X}+\mathrm{Z}}{2}=Y$
• From equation (1), $\frac{46}{2}=Y$, $Y=23$
• From equation (2), $Z-23=16$; $Z=39$
• Again from equation (1), $\mathrm{X}+39=46$; $\mathrm{X}=7$
• So, X, Y, and Z are Li, Na, and K respectively.