Tetrahedral Voids in an FCC Unit Cell
Locate tetrahedral voids in an FCC crystal, understand their geometry, and learn how they relate to real crystal structures like CaF2 and diamond.
About this simulation
- What
- An interactive Chemistry simulation of Tetrahedral 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 2026-02-13
Key Concepts
Tetrahedral Coordination
A tetrahedral void is surrounded by 4 atoms at the corners of a tetrahedron, giving a coordination number of 4.
Position & Count in FCC
In an FCC unit cell there are 8 tetrahedral voids, located at fractional coordinates such as (1/4, 1/4, 1/4).
Crystal Examples
CaF2 (fluorite) fills all 8 tetrahedral voids; Sphalerite (ZnS) fills only half (4) in an alternating pattern.
Understanding Tetrahedral Voids
Tetrahedral Voids are the smallest interstitial sites in a crystal lattice, formed by four adjacent spheres positioned at the vertices of a regular tetrahedron.
In a Face-Centered Cubic (FCC) unit cell, there are exactly eight tetrahedral voids. Each void is located at the center of the eight sub-cubes (octants) that comprise the main unit cell volume.
Use our interactive visualizer to explore how these voids define critical structures like Fluorite (CaF₂), Sphalerite (ZnS), and the Diamond lattice, where varying degrees of void occupancy dictate the material's properties.
Frequently Asked Questions
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