Correct order of first ionization energy of the following metals Na, Mg, Al, Si in `KJ mol^(–1)` respectively are:

Options

A. 786, 739, 577, 497
B. 497, 577, 737, 786
C. 497, 737, 577, 786
D. 739, 577, 786, 487

Answer

To determine the correct order of first ionization energy for the metals Na, Mg, Al, and Si, we will follow these steps:

### Step 1: Write the electronic configurations of the elements
- **Sodium (Na)**: The atomic number is 11, so its electronic configuration is \(1s^2 2s^2 2p^6 3s^1\) or in terms of the nearest noble gas, it is \([Ne] 3s^1\).
- **Magnesium (Mg)**: The atomic number is 12, so its electronic configuration is \(1s^2 2s^2 2p^6 3s^2\) or \([Ne] 3s^2\).
- **Aluminum (Al)**: The atomic number is 13, so its electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^1\) or \([Ne] 3s^2 3p^1\).
- **Silicon (Si)**: The atomic number is 14, so its electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^2\) or \([Ne] 3s^2 3p^2\).

### Step 2: Analyze the trend in ionization energy
- Ionization energy generally increases across a period (from left to right) due to the increase in nuclear charge which attracts the electrons more strongly, making them harder to remove.
- As we move from Na to Mg to Al to Si, we are moving from left to right across the third period.

### Step 3: Identify the exceptions
- While the general trend is that ionization energy increases from Na to Si, we need to consider the stability of electron configurations.
- Magnesium has a fully filled \(3s^2\) subshell, which provides extra stability, thus it will have a higher ionization energy than Aluminum, which has a \(3s^2 3p^1\) configuration.

### Step 4: Compare the ionization energies
- Based on the general trend and the exceptions:
- **Silicon (Si)** has the highest ionization energy due to its increased nuclear charge and electron configuration.
- **Magnesium (Mg)** follows next due to its stable filled subshell.
- **Aluminum (Al)** comes next as it has a higher ionization energy than Sodium.
- **Sodium (Na)** has the lowest ionization energy as it has only one electron in its outermost shell.

### Step 5: Arrange the elements in order of increasing ionization energy
- The order of first ionization energy from lowest to highest is:
- Na < Al < Mg < Si

### Step 6: Assign the values of ionization energy
- The first ionization energies in \(KJ mol^{-1}\) are approximately:
- Na: 497
- Al: 577
- Mg: 737
- Si: 786

### Final Answer
The correct order of first ionization energy of Na, Mg, Al, Si in \(KJ mol^{-1}\) is:
**Na (497) < Al (577) < Mg (737) < Si (786)**