Question

Briefly explain the first classification of elements and Mendeleev's periodic table.

Answer 1

Dobereiner triads:

• The first classification of elements was done by Dobereiner
• He tried to arrange the elements with similar properties into groups. He identified some groups having three elements each. So he called these groups ‘triads'.
• Dobereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

Mendeleev's periodic table:

• Prediction of new elements: The existence and properties of elements that are similar to Boron/Aluminum/Silicon is predicted by Mendeleev.
• “Mendeleev's Periodic Law states that the properties of elements are the periodic function of their relative atomic masses.”
• He left the gap after some elements and gave them hypothetical names such as Eka-Alumium/Eka-Silicon.
• He took more similarities in properties than to atomic mass in the arrangement such as Iodine I has a smaller weight than Tellurium Te but it was placed after it.
• From the periodic properties, Beryllium $\left(\mathrm{Be}\right)$, Indium $\left(\mathrm{In}\right)$, Gold $\left(\mathrm{Au}\right)$, and Platinum $\left(\mathrm{Pt}\right)$ were predicted to be having inaccurate mass which lead to the re-estimation of their real masses.