When a chlorine atom becomes chloride ion, its size — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

# Chlorine Atom to Chloride Ion: Size Change **Step 1: Electron configuration change** - Chlorine atom ($Cl$): 17 electrons, configuration ends in $3s^2 3p^5$ - Chloride ion ($Cl^-$): 18 electrons, configuration ends in $3s^2 3p^6$ (gains 1 electron) **Step 2: Effect of adding an electron** When $Cl$ gains an electron to form $Cl^-$: - Electron-electron repulsion increases (more electrons in same orbitals) - This repulsion pushes electrons further apart **Step 3: Nuclear charge stays constant** - Both $Cl$ and $Cl^-$ have 17 protons - The same nuclear charge cannot hold the increased number of electrons as tightly **Step 4: Net result** The increased electron-electron repulsion overcomes the constant nuclear attraction, causing electrons to spread out more. **Conclusion:** The size of chloride ion ($Cl^-$) is **larger than** the chlorine atom ($Cl$). --- **Answer B is correct because:** The chloride ion has a larger ionic radius than the neutral chlorine atom due to increased electron-electron repulsion from the additional electron, despite unchanged nuclear charge.