Question

Number of valence electrons in \(Cl^–\) ion are:

• A. 16
• B. 8
• C. 17
• D. 18

Answer 1

The Correct Option is B

To determine the number of valence electrons in the \(Cl^–\) (chloride anion), we must first understand the electronic configuration of chlorine.

1. Atomic Number of Chlorine: The atomic number of chlorine is 17, which means a neutral chlorine atom has 17 electrons.
2. Electronic Configuration: The electronic configuration of a neutral chlorine atom is: \(1s^2\,2s^2\,2p^6\,3s^2\,3p^5\).
3. Valence Electrons in Neutral Chlorine: The outermost shell (n=3) has 7 electrons (3s²3p⁵), so a neutral chlorine atom has 7 valence electrons. 
4. Formation of \(Cl^–\) Ion: When a chlorine atom gains an additional electron, it becomes a chloride ion (\(Cl^–\)). This additional electron is added to the 3p orbital, making the configuration:
5. \(1s^2\,2s^2\,2p^6\,3s^2\,3p^6\)

This configuration shows that the chloride ion now has a full outermost shell (3s²3p⁶), which totals 8 valence electrons.

Conclusion: Therefore, the number of valence electrons in \(Cl^–\) ion is 8.