Question

$\mathrm{Na}=\frac{\mathrm{Li}+\mathrm{K}}{2}=\frac{7+39}{2}=\frac{46}{2}=23$ What is dobereiners law of triads explain with the help of one example of dobereiners.

Answer 1

Triad

Triad is generally defined as a group of three elements.

Dobereiners law of triads

• Dobereiners arrange the elements in the form of traids.
• Nine elements were arranged in three traids.
• According to Dobereiner's law of triads, the arithmetic mean of the atomic masses of the first and third elements in a triad is almost equal to the atomic mass of the second element in that triad.
• As for Sodium ($\mathrm{Na}$) the atomic mass is the average of Lithium ($\mathrm{Li}$) and Potassium ($\mathrm{K}$) shown as:
• $\mathrm{Na}=\frac{\mathrm{Li}+\mathrm{K}}{2}=\frac{7+39}{2}=\frac{46}{2}=23$

Example

• With atomic masses of $40$, $88$, and $137$, respectively, the elements calcium ($\mathrm{Ca}$), strontium ($\mathrm{Sr}$), and barium ($\mathrm{Ba}$) constitute a triad because their chemical properties are similar.
• Strontium's atomic mass is roughly equal to the average of calcium and barium's atomic masses.