MCQ Detailed View

The electronic configuration of an atom shows the distribution of electrons in its atomic orbitals. For calcium (Ca), which has an atomic number of 20, the electrons fill the orbitals following the Aufbau principle, Hund’s rule, and Pauli exclusion principle.

The filling order is: 1s → 2s → 2p → 3s → 3p → 4s. Calcium has 20 electrons, so its configuration is written as:

1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

This configuration can also be expressed in noble gas shorthand using the previous noble gas, argon (Ar), which has 18 electrons. Therefore, the electronic configuration of Ca is [Ar] 4s².

Other options are incorrect:

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  [Ne] 4s² represents only 12 electrons (not 20).

  
  


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  [Ne] 4p² or [Kr] 4p² are configurations for other elements beyond calcium.

  
  

Understanding the electronic configuration is important in inorganic chemistry because it explains:

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  Chemical reactivity (Ca loses 2 electrons from 4s² to form Ca²⁺).

  
  


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  Position in the periodic table (group 2, alkaline earth metals).

  
  


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  Bonding behavior (ionic compounds like CaCl₂).

  
  


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  Magnetic and spectroscopic properties.

  
  

Calcium’s [Ar] 4s² configuration demonstrates that the outermost electrons occupy the 4s orbital, which are the valence electrons responsible for chemical reactions. This concept is foundational for students learning periodic trends, oxidation states, and metallic behavior.