The correct order of ionisation energy of C, N, O and F is

Options

A. `F lt N lt C lt O`
B. `C lt N lt O lt F`
C. `C lt O lt N lt F`
D. `F lt O lt N lt C`

Answer

To determine the correct order of ionization energy for the elements Carbon (C), Nitrogen (N), Oxygen (O), and Fluorine (F), we can follow these steps:

### Step 1: Understand Ionization Energy
Ionization energy is the minimum amount of energy required to remove the most loosely bound electron from an isolated gaseous atom. The higher the ionization energy, the more energy is required to remove an electron.

**Hint:** Remember that ionization energy increases as the attraction between the nucleus and the electrons increases.

### Step 2: Consider the Periodic Trends
Ionization energy generally increases across a period (from left to right) due to the increase in nuclear charge, which pulls the electrons closer to the nucleus, making them harder to remove. Conversely, ionization energy decreases down a group due to the increase in atomic size and the shielding effect.

**Hint:** Think about how atomic size and nuclear charge affect the ease of removing an electron.

### Step 3: Analyze the Elements in Question
- **Carbon (C)**: Atomic number 6, electronic configuration: 1s² 2s² 2p²
- **Nitrogen (N)**: Atomic number 7, electronic configuration: 1s² 2s² 2p³ (half-filled p-orbitals, more stable)
- **Oxygen (O)**: Atomic number 8, electronic configuration: 1s² 2s² 2p⁴
- **Fluorine (F)**: Atomic number 9, electronic configuration: 1s² 2s² 2p⁵

**Hint:** Pay attention to the electronic configurations, especially the stability of half-filled and fully filled orbitals.

### Step 4: Compare Ionization Energies
1. **Fluorine (F)** has the highest ionization energy because it has the highest nuclear charge and is closest to having a full outer shell.
2. **Nitrogen (N)** has a higher ionization energy than **Oxygen (O)** because of its half-filled p-orbitals, which provide extra stability, making it harder to remove an electron.
3. **Oxygen (O)** has a lower ionization energy than Nitrogen due to its higher electron-electron repulsion in the p-orbitals.
4. **Carbon (C)** has the lowest ionization energy among these elements as it has fewer protons attracting the electrons compared to the others.

**Hint:** Consider the stability provided by half-filled and fully filled orbitals when comparing nitrogen and oxygen.

### Step 5: Establish the Correct Order
Based on the above analysis, the correct order of ionization energy from highest to lowest is:
**F > N > O > C**

**Final Answer:** The correct order of ionization energy for C, N, O, and F is **F > N > O > C**.