According to molecular orbital theory, which of the following will not be a viable molecule?

Options

A. `H_(2)^(-)`
B. `H_(2)^(2-)`
C. `He_(2)^(2+)`
D. `He_(2)^(+)`

Explanation

To determine which molecule is not viable according to molecular orbital theory (MOT), we will calculate the bond order for each molecule given in the options. A bond order of 0 indicates that the molecule does not exist.

### Step-by-Step Solution:

1. **Identify the Molecule**: Let's analyze the first option, H2^(-) (hydride ion).

2. **Write the Electronic Configuration**:
- For H2^(-), the electronic configuration is:
- Bonding molecular orbital: σ1s² (2 electrons)
- Antibonding molecular orbital: σ*1s¹ (1 electron)
- Therefore, the electronic configuration is σ1s² σ*1s¹.

3. **Calculate the Bond Order**:
- Bond Order (B.O.) = (Number of electrons in bonding MOs - Number of electrons in antibonding MOs) / 2
- B.O. = (2 - 1) / 2 = 1 / 2 = 0.5

4. **Conclusion for H2^(-)**:
- Since the bond order is 0.5, H2^(-) exists.

5. **Analyze the Second Option**: Now, let's look at H2^(2-) (dihydride ion).

6. **Write the Electronic Configuration**:
- For H2^(2-), the electronic configuration is:
- Bonding molecular orbital: σ1s² (2 electrons)
- Antibonding molecular orbital: σ*1s² (2 electrons)
- Therefore, the electronic configuration is σ1s² σ*1s².

7. **Calculate the Bond Order**:
- B.O. = (Number of electrons in bonding MOs - Number of electrons in antibonding MOs) / 2
- B.O. = (2 - 2) / 2 = 0 / 2 = 0

8. **Conclusion for H2^(2-)**:
- Since the bond order is 0, H2^(2-) does not exist.

### Final Answer:
According to molecular orbital theory, H2^(2-) is the molecule that will not be a viable molecule.

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