Which period 3 element has the largest ionic radius?

• A. Mg
• B. Na
• C. S
• D. Cl

Answer: (C)

Verified step by step guidance

1. Understand that ionic radius depends on the charge of the ion and the number of electrons relative to protons. When elements form ions, they either lose or gain electrons, affecting their size.
2. Identify the common ions formed by the given period 3 elements: Na typically forms Na⁺, Mg forms Mg²⁺, S forms S²⁻, and Cl forms Cl⁻.
3. Recall that cations (positive ions) are smaller than their neutral atoms because they lose electrons, reducing electron-electron repulsion and allowing the nucleus to pull electrons closer.
4. Anions (negative ions) are larger than their neutral atoms because they gain electrons, increasing electron-electron repulsion and expanding the electron cloud.
5. Compare the ionic radii by considering the charge and electron configuration: S²⁻ has gained two electrons, increasing its size significantly compared to Na⁺, Mg²⁺, and Cl⁻, so S²⁻ has the largest ionic radius among the options.