Question

The correct statement for the molecule $Cs{{I}_{3}}$ is that:
(A) It contains $C{{s}^{3+}}$ and ${{I}^{-}}$ ions
(B) It contains $C{{s}^{+}}$,${{I}^{-}}$ and lattice ${{I}_{2}}$ molecule
(C) It is a covalent molecule
(D) It contains $C{{s}^{+}}$ and ${{I}_{3}}^{-}$ ions

Answer 1

Hint: Caesium is a group one element and iodine is a group seven element or halogen. Usually group one elements don't show +3 oxidation state. Like this we can examine each of the given options according to the properties of Caesium and iodine and we would be able to find the correct statement.

Complete step by step answer:
  - The $Cs{{I}_{3}}$ molecule is called as Caesium triiodide .Lets check each of the given statements and verify them.
 (i) It contains $C{{s}^{3+}}$and ${{I}^{-}}$ ions
 - Caesium is a group one element and group one element does not exhibit +3 oxidation states. Hence the possibility of forming $C{{s}^{3+}}$ is excluded and this option is incorrect.

(ii) It contains $C{{s}^{+}}$,${{I}^{-}}$ and lattice ${{I}_{2}}$ molecule
 - As we know iodine is a halogen molecule which is located at the right side of the periodic table and hence it is larger in size. Since ${{I}_{2}}$ molecule is large it cannot be accommodated in the crystal lattice of $Cs{{I}_{3}}$ molecule. Thus option (B) is wrong.

 (iii) It is a covalent molecule
-Cations are formed when a metal loses its valence electrons and an anion is formed when a nonmetal gains an electron and an ionic bond is formed as a result of the electrostatic force between them. . In the case of covalent bonds the electrons are shared between the two atoms.
-As we mentioned Caesium is a group one element (electropositive) and iodine is a halogen (highly electronegative).They always tend to form ionic bonds. Hence $Cs{{I}_{3}}$ is an ionic compound. Thus option (C) can be excluded.

(iv) It contains $C{{s}^{+}}$and ${{I}_{3}}^{-}$ ions
- $Cs{{I}_{3}}$ on dissociation gives $C{{s}^{+}}$ and ${{I}_{3}}^{-}$ and this ${{I}_{3}}^{-}$ on dissociation gives ${{I}_{2}}$ and ${{I}^{-}}$.This dissociation can be represented as follows
\[Cs{{I}_{3}}\to C{{s}^{+}}+{{I}_{3}}^{-}\]
\[{{I}_{3}}^{-}\to {{I}^{-}}+{{I}_{2}}\]
Thus this statement is correct.
So, the correct answer is “Option D”.

Note: Keep in mind that the molecular weight of Caesium triiodide is 513 grams. Also do not confuse Caesium iodide with Caesium triiodide. Caesium iodide has a molecular formula of CsI and Caesium triiodide has the molecular formula $Cs{{I}_{3}}$. Iodide is a monatomic, uni-negative anion and triiodide is a triatomic, uni-negative anion.