Which one of the following ions is not tetrahedral in shape?

Options

A. `CH_4`
B. `NH_(4)^(+)`
C. `BF_(4)^(-)`
D. `[Cu(NH_3)_(4)]^(2+)`

Explanation

To determine which ion is not tetrahedral in shape, we will analyze the hybridization and geometry of the given ions. The options provided are CH4, NH4^+, BF4^-, and a copper complex. Let's evaluate each one step by step.

### Step 1: Analyze CH4 (Methane)
1. **Valence Electrons**: Carbon (C) has 4 valence electrons.
2. **Monovalent Atoms**: There are 4 hydrogen (H) atoms attached.
3. **Charges**: There are no cationic or anionic charges.
4. **Steric Number Calculation**:
\[ \text{Steric Number} = \frac{(4 + 4 - 0 + 0)}{2} = \frac{8}{2} = 4 \]
5. **Hybridization**: With a steric number of 4, the hybridization is sp³.
6. **Shape**: The shape is tetrahedral.

### Step 2: Analyze NH4^+ (Ammonium Ion)
1. **Valence Electrons**: Nitrogen (N) has 5 valence electrons.
2. **Monovalent Atoms**: There are 4 hydrogen (H) atoms attached.
3. **Charges**: There is a +1 charge (cationic).
4. **Steric Number Calculation**:
\[ \text{Steric Number} = \frac{(5 + 4 - 1 + 0)}{2} = \frac{8}{2} = 4 \]
5. **Hybridization**: With a steric number of 4, the hybridization is sp³.
6. **Shape**: The shape is tetrahedral.

### Step 3: Analyze BF4^- (Boron Tetrafluoride Ion)
1. **Valence Electrons**: Boron (B) has 3 valence electrons.
2. **Monovalent Atoms**: There are 4 fluorine (F) atoms attached.
3. **Charges**: There is a -1 charge (anionic).
4. **Steric Number Calculation**:
\[ \text{Steric Number} = \frac{(3 + 4 + 1 + 0)}{2} = \frac{8}{2} = 4 \]
5. **Hybridization**: With a steric number of 4, the hybridization is sp³.
6. **Shape**: The shape is tetrahedral.

### Step 4: Analyze the Copper Complex (Cu^2+ with Ammonia)
1. **Valence Electrons**: Copper (Cu) in the +2 oxidation state has 9 d-electrons.
2. **Hybridization**: The complex involves hybridization of 4s and 3d orbitals due to the presence of ammonia as a ligand.
3. **Steric Number Calculation**: The hybridization here is dsp².
4. **Shape**: The shape of this complex is square planar, not tetrahedral.

### Conclusion
From the analysis, CH4, NH4^+, and BF4^- all have tetrahedral shapes, while the copper complex has a square planar shape. Thus, the ion that is **not tetrahedral in shape** is the **copper complex**.