In solid state, `PCl_(5)` is a……..

Options

A. convalent solid
B. octahedral structure
C. ionic solid with `[PCl_(6)]^(+)` octahedral and `[PCl_(4)]^(-)` tetrahedral
D. ionic solid with `[PCl_(4)]^(+)` tetrahedral and `[PCl_(6)]^(-)` octahedral

Explanation

To determine the nature of solid-state PCl₅, we can analyze its structure and bonding. Here’s a step-by-step solution:

### Step 1: Understanding the Composition of PCl₅
PCl₅ (phosphorus pentachloride) is a chemical compound made up of one phosphorus atom and five chlorine atoms. In the solid state, it does not remain as discrete PCl₅ molecules.

**Hint:** Consider how molecules interact in the solid state and whether they remain intact or form new structures.

### Step 2: Analyzing the Solid-State Structure
In the solid state, PCl₅ can dissociate into ions. It forms a pair of ions: PCl₄⁺ (tetrahedral) and PCl₆⁻ (octahedral). This dissociation occurs because one PCl₅ molecule can lose a chloride ion (Cl⁻), resulting in a PCl₄⁺ ion, while the lost chloride ion is gained by another PCl₅ molecule, forming the PCl₆⁻ ion.

**Hint:** Think about how ionic compounds are formed and how charge balance is maintained.

### Step 3: Identifying the Geometry of the Ions
- **PCl₄⁺ Ion:** This ion has four chlorine atoms bonded to a central phosphorus atom. The geometry is tetrahedral due to the arrangement of the four bond pairs around phosphorus.
- **PCl₆⁻ Ion:** This ion has six chlorine atoms bonded to phosphorus, resulting in an octahedral geometry because of the six bond pairs.

**Hint:** Recall the VSEPR theory, which helps predict the geometry of molecules based on the number of bonds and lone pairs.

### Step 4: Classifying the Solid-State Form
Since PCl₅ in solid state exists as PCl₄⁺ and PCl₆⁻, it is classified as an ionic solid. The presence of positively and negatively charged ions indicates that the structure is ionic rather than covalent.

**Hint:** Consider the definitions of ionic and covalent solids and how the presence of charged ions influences the classification.

### Conclusion
In solid state, PCl₅ exists as an ionic solid composed of PCl₄⁺ (tetrahedral) and PCl₆⁻ (octahedral) ions.

**Final Answer:** In solid state, PCl₅ is an ionic solid with PCl₄⁺ (tetrahedral) and PCl₆⁻ (octahedral).

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