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: Determine electron configuration changes** - Chlorine atom ($Cl$): $1s^2 2s^2 2p^6 3s^2 3p^5$ (17 electrons, 17 protons) - Chloride ion ($Cl^-$): $1s^2 2s^2 2p^6 3s^2 3p^6$ (18 electrons, 17 protons) **Step 2: Analyze electron-proton ratio** - $Cl$ atom: 17 protons attracting 17 electrons → moderate nuclear pull per electron - $Cl^-$ ion: 17 protons attracting 18 electrons → nuclear pull is now spread over more electrons **Step 3: Apply electron shielding principle** - Adding an extra electron increases electron-electron repulsion - The effective nuclear charge ($Z_{eff}$) per electron decreases - Outer electrons are held less tightly **Step 4: Conclusion** The chloride ion has **increased in size** compared to the chlorine atom because: - More electrons repel each other - Lower effective nuclear charge per electron - Electrons occupy a larger orbital **Answer B is correct:** The size **increases** when $Cl \rightarrow Cl^-$