Which electronic configuration corresponds to an element of Group IIIA?

Elements of Group IIIA (Group 13) in the periodic table include boron (B), aluminium (Al), gallium (Ga), indium (In), and thallium (Tl). A defining feature of this group is that all elements have three valence electrons, with a general outer shell configuration of ns² np¹. This configuration determines their chemical properties, such as forming trivalent cations (M³⁺) and forming covalent or metallic bonds.

The given electronic configuration:

1s² 2s² 2p⁶ 3s² 3p¹

can be broken down as:

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  Core electrons: 1s² 2s² 2p⁶ (total 10 electrons, corresponding to the neon core)

  
  


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  Valence electrons: 3s² 3p¹ (three electrons in the third shell)

  
  

This matches the ns² np¹ pattern typical of Group IIIA elements. Specifically, this configuration belongs to aluminium (Al), which is the third element in Group IIIA. Its three valence electrons explain its trivalent behavior in compounds like AlCl₃ and Al₂O₃.

Other options:

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  1s² 2s² 2p³ → Group VA (5 valence electrons, e.g., nitrogen)

  
  


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  1s² 2s² 2p⁴ → Group VIA (6 valence electrons, e.g., oxygen)

  
  


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  1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹ → Group IIIB transition metal (scandium, not IIIA)

  
  

Thus, the correct configuration representing a Group IIIA element is 1s² 2s² 2p⁶ 3s² 3p¹, illustrating how valence electron arrangement defines group behavior, periodic properties, and chemical reactivity in inorganic chemistry