Which of the following species has the highest electron affinity?

Options

A. `F^(-)`
B. `O`
C. `O^(-)`
D. `Na^(+)`

Explanation

To determine which species has the highest electron affinity among the given options, we need to understand the concept of electron affinity and how it relates to atomic size and electron configuration. Here’s a step-by-step solution:

### Step 1: Understand Electron Affinity
Electron affinity is defined as the amount of energy released when an electron is added to an isolated gaseous atom. Generally, elements with a higher tendency to gain electrons have higher electron affinity.

**Hint:** Remember that electron affinity is related to how easily an atom can accept an additional electron.

### Step 2: Consider Atomic Size
The size of the atom plays a crucial role in determining electron affinity. Smaller atoms tend to have higher electron affinity because the added electron is closer to the nucleus and experiences a stronger attraction.

**Hint:** Smaller atomic size leads to a higher nuclear charge effect on the added electron, increasing electron affinity.

### Step 3: Analyze the Given Species
Let’s analyze the species mentioned:
- Sodium ion (Na⁺): This species has lost an electron and thus has a positive charge. It does not have a tendency to gain an electron.
- Oxygen (O): It has an electron configuration of 1s² 2s² 2p⁴. It can gain an electron to achieve a stable configuration (1s² 2s² 2p⁵).
- O⁻ (Oxygen anion): This species has already gained an electron, making it less likely to gain another due to electron-electron repulsion.
- F⁻ (Fluoride ion): Similar to O⁻, it has a full outer shell (1s² 2s² 2p⁶) and is also less likely to gain another electron.

**Hint:** Focus on the neutral atoms and their ability to gain electrons rather than the ions.

### Step 4: Compare Electron Affinity
Now, we compare the electron affinity of O and F:
- Oxygen (O) can gain an electron to become O⁻, which is energetically favorable.
- Fluorine (F) has a very high electron affinity, but F⁻ is already stable and less likely to accept another electron.

**Hint:** Remember that the stability of the anions (O⁻ and F⁻) reduces their ability to gain additional electrons.

### Step 5: Conclusion
Among the species analyzed, the neutral oxygen atom (O) has the highest electron affinity because it can effectively gain an electron to achieve a stable configuration, while the other species either have a positive charge or are already negatively charged and stable.

**Final Answer:** The species with the highest electron affinity is **Oxygen (O)**.