Question

Explain electronic configuration of He and N according to Pauli and Hund’s principle.

Answer 1

Pauli's Principle:

This principle states that two electrons cannot have all the same Quantum numbers.

Hund's Principle:

This principle states that electrons will first occupy the orbitals singly and then undergo pairing.

Following these principles:

Helium has atomic number 2. Hence these two electrons occupy the 1s orbital in pair.

\begin{gathered} \{He \}_{2} = \: \{ \uparrow \downarrow \} \\ \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: 1 {s}^{2} \end{gathered}

{He}

2

={↑↓}

1s

2

Nitrogen has atomic number 7.

\begin{gathered} \{N \}_{7} = \: \{ \uparrow \downarrow \} \: \: \{ \uparrow \downarrow \} \: \: \{ \uparrow \uparrow \uparrow \}\\ \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: 1 {s}^{2} \: \: \: 2 {s}^{2} \: \: \: \: \: 2 {p}^{3} \end{gathered}

{N}

7

={↑↓}{↑↓}{↑↑↑}

1s

2

2s

2

2p

3

Hence , first two electrons occupy the 1s orbital, second to electron occupy the 2s orbital. And last three electron occupy the 2p orbital without pairing.