Chapter 8, Problem 8.3P

(a)

Interpretation Introduction

Interpretation:

The predicted atomic mass of $\text{K}$ from the atomic masses of $\text{Na}$ and $\text{Rb}$ with the use of Dobereiner’s triads is to be determined.

Concept introduction:

Dobereiner stated that all elements occur in the groups of three when arranged in the increasing order of their atomic masses. Such groups of three elements were called triads which have similar chemical properties.

The triads can be used to calculate the atomic mass of the middle element by the average of the elements which lie above and below the given element.

(b)

Interpretation Introduction

Interpretation:

The predicted melting point of ${\text{Br}}_2$ from the melting points of ${\text{Cl}}_2$ and ${\text{I}}_2$ is to be determined

Concept introduction:

Dobereiner stated that all elements occur in the groups of three when arranged in the increasing order of their atomic masses. Such groups of three elements were called triads.

The triads can be used to predict the chemical properties of the elements.such as melting and boiling points. According to Dobereiner the boiling or melting point of the middle element can be calculated by taking the average of the first and third element in a given triad.