Chapter 12, Problem 1ASA

As pure elements, all of the halogens are diatomic molecular species. Their melting points are: ${\text{F}}_{\text{2}}$. $\text{54}\text{K}$; ${\text{Cl}}_{\text{2}}$, $\text{172}\text{K}$; ${\text{Br}}_{\text{2}}$,. $\text{266}\text{K}$; and ${\text{I}}_{\text{2}}$, $\text{387}\text{K}$. Using the Periodic Table, predict as best you can the molecular formula of elemental astatine, $\text{At}$, the only radioactive element in this family. Also predict whether it will be a solid, liquid, or gas at room temperature.

Elemental formula: ______ Phase at room temperature: ______

Interpretation Introduction

Interpretation:

The elemental formula and phase of elemental astatine are to be stated.

Concept introduction:

The periodic table is an important part of chemistry. In this table, all known elements are arranged on the basis of their atomic number. Elements having same outer electronic configuration are kept in same groups. The elements on left of periodic table are metals, on right are nonmetals and in center are transition metals and metalloids.

Answer to Problem 1ASA

The elemental formula of astatine is ${\text{At}}_{\text{2}}$ and it occurs as a solid at room temperature.

Explanation of Solution

The elemental forms of other members of astatine group are ${\text{F}}_{\text{2}}$, ${\text{Cl}}_{\text{2}}$, ${\text{Br}}_{\text{2}}$ and ${\text{I}}_{\text{2}}$. So, the elemental formula of astatine is ${\text{At}}_{\text{2}}$.

The melting points of ${\text{F}}_{\text{2}}$, ${\text{Cl}}_{\text{2}}$, ${\text{Br}}_{\text{2}}$ and ${\text{I}}_{\text{2}}$ are $\text{54}\text{K}$, $\text{172}\text{K}$, $\text{266}\text{K}$ and $\text{387}\text{K}$ respectively. This means ${\text{F}}_{\text{2}}$ and ${\text{Cl}}_{\text{2}}$ exists in gas phase, ${\text{Br}}_{\text{2}}$ exists in liquid phase and ${\text{I}}_{\text{2}}$ exists in solid phase at room temperature that is at $273\text{K}$.

Since astatine is present after iodine in the group, therefore, its melting point is higher than $\text{387}\text{K}$.

So, ${\text{At}}_{\text{2}}$ exists in solid phase at room temperature.

Conclusion

The elemental formula of astatine is ${\text{At}}_{\text{2}}$ and it exists as solid at room temperature.