Octahedral Voids in an FCC Unit Cell
Locate octahedral voids in an FCC crystal, understand their geometry, and connect them to NaCl-type structures.
About this simulation
- What
- An interactive Chemistry simulation of Octahedral Voids in an FCC Unit Cell.
- Who
- Designed for AP, IB, and A‑Level Chemistry students.
- How
- Runs in any modern browser — drag, adjust, and explore in real time.
Updated 2026-02-12
Key Concepts
Octahedral Coordination
An octahedral void is surrounded by 6 atoms, giving a coordination number of 6.
Position & Count in FCC
In an FCC unit cell there are 4 octahedral voids: 1 at the body center and 12 at edge centers shared by 4 cells.
Crystal Examples
NaCl is a classic structure where the anions form an FCC lattice and the cations occupy all octahedral voids.
Understanding Octahedral Voids
Octahedral Voids are the interstitial spaces in a crystal lattice surrounded by six nearest-neighbor atoms. In a Face-Centered Cubic (FCC) unit cell, these voids are systematically positioned at the body center and at the center of each of the twelve edges.
The geometry of an octahedral void is defined by a coordination number of 6. Each FCC unit cell contains a total of four octahedral voids (1 body-center void + 12 × 1/4 edge-center voids), matching the number of lattice atoms per cell.
Explore our interactive model to visualize how iconic structures like Sodium Chloride (NaCl) are assembled, where larger ions form the FCC framework while smaller ions occupy all available octahedral voids.
Frequently Asked Questions
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