Arrange these ions according to ionic radius. Largest radius Smallest radius Answer Bank S2- K+ Ca2+ p3- CI-
Arrange these ions according to ionic radius.
The Correct Answer and Explanation is:
Correct Order (from Largest Radius to Smallest Radius):
P³⁻ > S²⁻ > Cl⁻ > K⁺ > Ca²⁺
Explanation
Ionic radius refers to the size of an ion, which depends on the number of electrons, the nuclear charge (number of protons), and the electron-electron repulsion within an atom or ion.
To arrange the given ions (S²⁻, K⁺, Ca²⁺, P³⁻, Cl⁻) by ionic radius, we consider two main factors:
- Electron gain or loss (charge of the ion)
- Number of protons (nuclear charge)
Step 1: Determine electron configurations
All of these ions are isoelectronic—they have the same number of electrons (18 electrons, like Argon) but different numbers of protons.
- P³⁻: 15 protons, 18 electrons
- S²⁻: 16 protons, 18 electrons
- Cl⁻: 17 protons, 18 electrons
- K⁺: 19 protons, 18 electrons
- Ca²⁺: 20 protons, 18 electrons
Step 2: Compare nuclear charge
All ions have the same number of electrons, so the number of protons will determine how strongly the nucleus pulls those electrons inward.
- Fewer protons = weaker pull = larger radius
- More protons = stronger pull = smaller radius
Step 3: Arrange by size
- P³⁻ has the fewest protons (15) → largest ionic radius
- S²⁻ (16 protons) → slightly smaller
- Cl⁻ (17 protons) → smaller
- K⁺ (19 protons) → smaller still
- Ca²⁺ has the most protons (20) → smallest ionic radius
Also, cations (positive ions like K⁺, Ca²⁺) are smaller than their parent atoms because they lose electrons, reducing electron repulsion and allowing the nucleus to pull remaining electrons in closer. Anions (negative ions like P³⁻, S²⁻) are larger because they gain electrons, increasing electron repulsion and expanding the cloud.
Final Order:
➡️ P³⁻ > S²⁻ > Cl⁻ > K⁺ > Ca²⁺
From largest to smallest ionic radius.
