If the nitrogen atom has electronic configuration `1s^(7)`, it would have energy lower than that of the normal ground state configuration `1s^(2)2s^(2)2p^(3)` because the electrons would be closer to the nucleus. Yet `1s^(7)` is not observed because it violates

Options

A. Heisenberg uncertainty principle
B. Hund’s rule
C. Pauli exclusion principle
D. Bohr postulate of stationary orbits

Explanation

To solve the question regarding why the electronic configuration `1s^(7)` for a nitrogen atom is not observed, we can break down the explanation step by step.

### Step 1: Understanding the Ground State Configuration
The normal ground state electronic configuration of a nitrogen atom is `1s^(2) 2s^(2) 2p^(3)`. This means nitrogen has:
- 2 electrons in the 1s orbital
- 2 electrons in the 2s orbital
- 3 electrons in the 2p orbital

### Step 2: Hypothetical Configuration `1s^(7)`
The question posits a hypothetical configuration of `1s^(7)`. This implies that there are 7 electrons in the 1s orbital.

### Step 3: Energy Consideration
While it may seem that having more electrons in the 1s orbital would lower the energy of the atom because these electrons are closer to the nucleus, this configuration is not physically realizable.

### Step 4: Pauli's Exclusion Principle
The key reason `1s^(7)` is not observed is due to **Pauli's Exclusion Principle**. This principle states that no two electrons in an atom can have the same set of four quantum numbers.

### Step 5: Quantum Numbers for `1s^(7)`
For the 1s orbital:
- Principal quantum number (n) = 1
- Azimuthal quantum number (l) = 0
- Magnetic quantum number (m_l) = 0
- Spin quantum number (m_s) can be either +1/2 or -1/2

If we try to fill the 1s orbital with 7 electrons:
1. The first electron can have quantum numbers (1, 0, 0, +1/2).
2. The second electron can have quantum numbers (1, 0, 0, -1/2).
3. For the third electron, we would have to repeat one of the previous quantum numbers, which means it would have the same set of quantum numbers as one of the first two electrons.

### Step 6: Violation of the Principle
Since we cannot assign unique quantum numbers to all 7 electrons in the 1s orbital without repeating, this violates Pauli's Exclusion Principle. Therefore, the configuration `1s^(7)` is not possible.

### Conclusion
Thus, the reason why `1s^(7)` is not observed for nitrogen is that it violates Pauli's Exclusion Principle.

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