* Effective Nuclear Charge: Chloride ions (Cl-) have a greater effective nuclear charge than sodium ions (Na+). Effective nuclear charge is the net positive charge experienced by an electron in an atom. With chlorine, the nucleus has more protons, which pulls the electrons in more tightly. This results in a smaller ionic radius.
* Electron Configuration: Chlorine (Cl) has one more electron shell than sodium (Na) in its neutral state. When chlorine gains an electron to become Cl-, it fills its outermost shell. Sodium loses an electron to become Na+, leaving it with a completely filled inner shell. This full outer shell in chloride makes it more compact.
* Number of Electrons: Chloride ions have 18 electrons, while sodium ions have 10 electrons. The greater number of electrons in chloride ion creates a greater repulsion between the electrons, which slightly expands the ion's radius. However, the effect of effective nuclear charge is much stronger, leading to a smaller overall ionic radius.
In summary: The greater effective nuclear charge and the filled outer shell in chloride ions contribute to a smaller ionic radius compared to sodium ions.
