MCQ Detailed View

Sodium (Na) is an element with atomic number 11. This means it has 11 protons in its nucleus and, in a neutral atom, 11 electrons surrounding the nucleus. The arrangement of these electrons in different shells and orbitals is called the electronic configuration.

The filling of electrons follows the Aufbau principle, Pauli exclusion principle, and Hund’s rule. According to these rules, electrons occupy orbitals in order of increasing energy levels. The sequence is: 1s → 2s → 2p → 3s → 3p → 4s, and so on.

For sodium:

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  The first shell (K shell) can hold 2 electrons, so we place 2 electrons in 1s orbital → 1s².

  
  


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  The second shell (L shell) can hold up to 8 electrons. We fill 2 electrons in 2s orbital → 2s², and 6 electrons in 2p orbital → 2p⁶. At this point, 10 electrons are filled.

  
  


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  Sodium has one electron left, which goes into the 3s orbital → 3s¹.

  
  

Thus, the complete electronic configuration of sodium is: 1s² 2s² 2p⁶ 3s¹.

This configuration shows that sodium has a single electron in its outermost shell (3rd shell). That single 3s¹ electron is very loosely bound, which makes sodium highly reactive. It tends to lose this one electron to achieve a stable configuration like neon (1s² 2s² 2p⁶), which is a noble gas with a full outer shell.

This is why sodium usually forms a +1 cation (Na⁺). In chemical reactions, sodium readily combines with other elements, such as chlorine, to form ionic compounds like sodium chloride (NaCl).

In summary, the electronic configuration of sodium is 1s² 2s² 2p⁶ 3s¹, which explains its chemical reactivity and its position in Group 1 (alkali metals) of the periodic table.