CBSE Class 9 Answered

• Valence electrons are the total number of electrons present in the valence shell or outermost shell.
• The atomic number of chlorine is 17.
• The electronic configuration is 2, 8, 7.
• Hence, there are 7 electrons in the valence shell of chlorine.
• Chlorine it accepts an electron to form a chloride ion as follows:

          Cl + e^- → Cl^-

• On accepting an electron, chlorine forms chloride ion which has one electron more than chlorine atom.
• Thus, the electronic configuration of chloride ion becomes 2, 8, 8.
• Hence, there are 8 electrons in the valence shell of  Cl^- ion.