Question

Which of the following is correct for $Tl{I_3}$?

A) An ionic compound consisting of $T{l^{3 + }}$ and three $3{I^ - }$ ions

B) A covalent compound

C) An ionic compound consisting of $T{l^ + }$ and $I_3^ -$ ions

D) A mixture of $TlI$ and ${I_2}$

Answer 1

As we know that Thallium halides mainly involves the monohalides and thallium is generally found in $+ 1$ oxidation states. Thallium trihalides are comparatively less stable than the other members of the group. But this compound is never present in $+ 3$ oxidation state.

Complete answer:

We are very well aware of the compounds formed by the element thallium which generally exists with halides as monohalides possessing $+ 1$ oxidation states. Thallium is chemically quite distinct and is comparatively less stable when compared to Aluminium, gallium and indium.

The triiodide in these compounds does not have $+ 3$ oxidation states of thallium due to the instability reasons but is present as compounds having $+ 1$ oxidation states of thallium and linearly present triiodide ion as $I_3^ -$ ion.

Thallium triiodide or $Tl{I_3}$ is produced as a result of reaction between the thallium iodide and iodine element and is a black crystalline solid. We can show this reaction with the help of an equation as:

$TlI + {I_2} \to T{l^ + } + I_3^ -$

Thus we can say that Thallium triiodide is a mixture of $TlI$ and ${I_2}$and is an ionic compound consisting of $T{l^ + }$ and $I_3^ -$ ions.

Hence, the correct answer is Option C and D.

Note: Remember that thallium triiodide has a similar structure as ammonium triiodide, rubidium triiodide and cesium triiodide and the triiodide ion in these compounds is nearly linear but becomes asymmetric because one iodide-iodide bond is longer than the other two bonds in the compound. Thallium triiodide can also be prepared by the mixture of thallium iodide and iodine in the presence of ethanol and aqueous hydrogen iodide gas.