Which of the following ions is most unlikely to exist?

Options

A. `Li^(-)`
B. `Be^(-)`
C. `B^(-)`
D. `F^(-)`

Answer

To determine which of the following ions is most unlikely to exist, we will analyze the electronic configurations of the given elements and their corresponding ions. The options provided are Lithium ion (Li⁻), Beryllium ion (Be²⁻), Boron ion (B³⁻), and Chlorine ion (Cl⁻).

### Step 1: Identify the electronic configurations of the elements.

1. **Lithium (Li)**: Atomic number = 3
- Electronic configuration: 1s² 2s¹

2. **Beryllium (Be)**: Atomic number = 4
- Electronic configuration: 1s² 2s²

3. **Boron (B)**: Atomic number = 5
- Electronic configuration: 1s² 2s² 2p¹

4. **Chlorine (Cl)**: Atomic number = 17
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁵

### Step 2: Determine the ions formed from these elements.

- **Lithium ion (Li⁻)**: Gains 1 electron.
- New configuration: 1s² 2s² (which is stable).

- **Beryllium ion (Be²⁻)**: Gains 2 electrons.
- New configuration: 1s² 2s² 2p² (this configuration is not stable as it exceeds the stable filled orbitals).

- **Boron ion (B³⁻)**: Gains 3 electrons.
- New configuration: 1s² 2s² 2p⁴ (this configuration is also not stable as it does not fill the p orbital completely).

- **Chlorine ion (Cl⁻)**: Gains 1 electron.
- New configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ (which is stable).

### Step 3: Analyze the stability of the ions.

- **Lithium ion (Li⁻)**: Stable because it achieves a filled outer shell.
- **Beryllium ion (Be²⁻)**: Unstable because it has an incomplete p orbital and is not favorable for beryllium to gain electrons.
- **Boron ion (B³⁻)**: Unstable as it also does not achieve a completely filled p orbital.
- **Chlorine ion (Cl⁻)**: Stable because it achieves a filled outer shell.

### Conclusion

Among the ions listed, the **Beryllium ion (Be²⁻)** is the most unlikely to exist due to its already filled 1s² and 2s² orbitals, making it unfavorable for the atom to gain additional electrons.

### Final Answer: Beryllium ion (Be²⁻)

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