`AlCl_(3)` is an electron-deficient compound but `AlF_(3)` is not, due to

Options

A. Atomic size of `F` is smaller than `Cl`, which makes `AlF_(3)` more covalent.
B. `AlCl_(3)` is a covalent compound compound while `AlF_(3)` is an ionic compound.
C. `Al` in `AlCl_(3)` is `sp^(3)` hybridised but in `AlF_(3), Al` is `sp^(3)` hybridised.
D. `AlCl_(3)` exists as a dimer but `AlF_(3)` does not.

Answer

To understand why AlCl₃ is an electron-deficient compound while AlF₃ is not, we can break down the reasoning into several steps:

### Step 1: Understand the Compounds
- **AlCl₃ (Aluminum Chloride)** and **AlF₃ (Aluminum Fluoride)** are both compounds of aluminum with different halogens (chlorine and fluorine).
- AlCl₃ is known to be electron-deficient, meaning it does not have a complete octet around the aluminum atom.
- AlF₃, on the other hand, does not exhibit this electron deficiency.

**Hint:** Consider the electron configurations and bonding nature of aluminum with different halogens.

### Step 2: Analyze the Ionic and Covalent Character
- The nature of bonding in these compounds can be influenced by the size and electronegativity of the anions (Cl⁻ and F⁻).
- Chlorine is larger and less electronegative than fluorine, which affects the type of bond formed with aluminum.

**Hint:** Recall how ionic and covalent character is determined by the size of ions and their electronegativities.

### Step 3: Apply Pauling's Rule
- According to Pauling's rule, the ionic character of a compound increases with the size of the anion and decreases with the size of the cation.
- In this case, aluminum (the cation) is the same in both compounds, but the size of the anions differs.

**Hint:** Think about how the relative sizes of cations and anions influence the bond type.

### Step 4: Compare the Sizes of Chlorine and Fluorine
- Chlorine (Cl) is larger than fluorine (F). This larger size leads to a more significant covalent character in AlCl₃ compared to AlF₃.
- The smaller size of fluorine allows for a stronger ionic bond in AlF₃, making it less electron-deficient.

**Hint:** Consider how the size of the anion affects the bond formation and electron sharing.

### Step 5: Conclusion
- AlCl₃ has a covalent character due to the larger size of the chloride ion, leading to electron deficiency.
- AlF₃, with the smaller fluoride ion, forms a more stable ionic bond, thus not being electron-deficient.

**Final Answer:** AlCl₃ is an electron-deficient compound due to its covalent character arising from the larger size of the chloride ion, while AlF₃ is not electron-deficient because it has a stronger ionic character due to the smaller fluoride ion.