Intermediate Topic 84 of 1102 Atomic Structure & Periodicity
Ionic Radius
The size of an ion; cations are smaller and anions larger than their parent atoms.
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In-depth explanation of Ionic Radius
Ionic radius describes the size of an ion. Cations are smaller than their parent atoms because the outermost shell is lost and the remaining electrons are pulled more tightly by the nucleus. Anions are larger than their parent atoms because the added electrons repel one another and expand the electron cloud. A higher positive charge on a cation gives a smaller radius, while a more negative anion is larger. Ionic radii are used to predict lattice energies and crystal structures.
Going deeper: Ionic Radius
Key ideas: Cations are smaller than their atoms (fewer electrons, lost shell, higher Z_eff): Na 186 pm to Na+ 102 pm. Anions are larger (more electron repulsion): Cl 99 pm to Cl- 181 pm. For the same element, higher positive charge gives smaller radius: Fe3+ less than Fe2+. Radius increases down a group and values depend on coordination number.
Common mistakes and connections: Students think ions have the same size as their parent atoms or that cations and anions of the same period follow one trend; there is a jump between cations and anions. Ionic radius governs lattice energy (proportional to 1 / (r+ + r-)), and so melting point and solubility of ionic solids.
Visualization of Ionic Radius
A cation is much smaller than its atom (Na 186 to Na+ 102 pm) while an anion is larger (Cl 99 to Cl- 181 pm). The interactive lesson shows this as a live animation or chart.
Worked example and use case
Sodium's atomic radius is about 186 pm, but Na+ is about 102 pm, while the chloride ion Cl- is about 181 pm, much larger than the covalent radius of chlorine at about 99 pm.
Frequently asked questions about Ionic Radius
What is Ionic Radius?
The size of an ion; cations are smaller and anions larger than their parent atoms.
Is Ionic Radius a beginner, intermediate or advanced topic?
Ionic Radius is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
What should I learn before Ionic Radius?
Study these earlier topics in Atomic Structure & Periodicity first: f-Block Elements, Metals Nonmetals and Metalloids, Atomic Radius.
What comes after Ionic Radius?
The next topics in Atomic Structure & Periodicity are Isoelectronic Species and Ionization Energy.
Can I practise Ionic Radius with quizzes?
Yes. The interactive lesson includes a self-check question on Ionic Radius, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Where Ionic Radius fits in Atomic Structure & Periodicity
Ionic Radius is topic 84 of 115 in Atomic Structure & Periodicity.