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An atom of element with the configuration 1S\(^2\)2S\(^2\)2P\(^6\)3S\(^2\)3P\(^5\) is likely to belong to

Chemistry
JAMB 2025

An atom of element with the configuration 1S\(^2\)2S\(^2\)2P\(^6\)3S\(^2\)3P\(^5\) is likely to belong to

  • A. group 7
  • B. group 5
  • C. group 2
  • D. group 3
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Correct Answer: Option A
Explanation

The electron configuration provided is 1s² 2s² 2p⁶ 3s² 3p⁵.

The outermost energy level (principal quantum number n = 3, or the third shell) contains the valence electrons.

To find the number of valence electrons, the electrons in the 3s and 3p sub-shells are summed: 2 + 5 = 7 valence electrons. Elements with 7 valence electrons in their outermost shell belong to Group 7 (or Group 17 in modern IUPAC notation) of the periodic table, known as the halogens.

The element with this configuration is chlorine (atomic number 17). 

The correct option is A - Group 7

There is an explanation video available below.


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Explanation Video

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