Ionic Radius Calculator
Compare ionic radii, calculate bond lengths, and predict coordination geometry using radius ratios.
Select Ions
Common Ionic Compounds:
Ionic Bond Length
283 pm
Predicted Geometry: Octahedral
+Na+ Radius
102 pm
-Cl- Radius
181 pm
r+/r-Radius Ratio
0.564
CNCoord. Number
6
Size Change from Neutral Atom:
Na+:
-46.3%
(Cations shrink)
Cl-:
+129.1%
(Anions expand)
Radius Ratio Rules
| Radius Ratio | CN | Geometry | Example |
|---|---|---|---|
| < 0.155 | 2 | Linear | BeF2 |
| 0.155 - 0.225 | 3 | Trigonal Planar | BN |
| 0.225 - 0.414 | 4 | Tetrahedral | ZnS |
| 0.414 - 0.732 | 6 | Octahedral | NaCl |
| > 0.732 | 8 | Cubic | CsCl |
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Editorial Note
MyCalcBuddy Editorial Team
This page is maintained as an educational calculator reference.
📚
Formula Source: Chemistry: The Central Science
by Brown, LeMay, Bursten
🔄Last reviewed: May 2026
✓Formula checks are based on standard references and internal QA review.