The `Ca^(2+)` and `F^(-)` ions arc located in `CaF_(2)` crystal respectively at what position ? What is the charge ratio ?

Options

A. FCC lattice , tetrahedral voids , 2 : 1
B. FCC lattice , half of tetrahedral voids , 1 : 2
C. BCC lattice , octahedral voids , 2 : 1
D. FCC lattice , half of octahedral voids , 1 : 2

Explanation

To solve the question regarding the positions of `Ca^(2+)` and `F^(-)` ions in the `CaF2` crystal and the charge ratio, we can follow these steps:

### Step 1: Identify the Structure of `CaF2`
`CaF2` is an ionic compound composed of calcium ions (`Ca^(2+)`) and fluoride ions (`F^(-)`). The structure of `CaF2` can be understood by recognizing that it forms a face-centered cubic (FCC) lattice.

**Hint:** Remember that in ionic compounds, cations and anions arrange themselves in a way that minimizes repulsion and maximizes attraction.

### Step 2: Determine the Positions of `Ca^(2+)` and `F^(-)` Ions
In the `CaF2` crystal structure:
- The `Ca^(2+)` ions occupy the lattice points of the FCC structure.
- The `F^(-)` ions occupy the tetrahedral voids in the FCC lattice.

**Hint:** The size of the ions influences their positions; larger cations typically occupy lattice points, while smaller anions occupy voids.

### Step 3: Understand the Coordination Numbers
- The coordination number of the `Ca^(2+)` ion in the FCC lattice is 8.
- The coordination number of the `F^(-)` ion in the tetrahedral void is 4.

**Hint:** Coordination number refers to the number of nearest neighbors surrounding an ion in the lattice.

### Step 4: Calculate the Charge Ratio
The charge of `Ca^(2+)` is +2 and the charge of `F^(-)` is -1. The charge ratio can be expressed as:
- Charge ratio = Charge of `Ca^(2+)` : Charge of `F^(-)` = 2 : 1

**Hint:** The charge ratio reflects the stoichiometry of the compound; it indicates how many anions are needed to balance the charge of the cations.

### Step 5: Summarize the Findings
- Positions: `Ca^(2+)` ions are at the FCC lattice points, and `F^(-)` ions are in the tetrahedral voids.
- Charge Ratio: The charge ratio is 2:1.

**Final Answer:**
- Positions: `Ca^(2+)` at FCC lattice points, `F^(-)` in tetrahedral voids.
- Charge Ratio: 2:1.