Chemistry Unit 1: Tetrahedral and Octahedral Voids

Study Notes

Tetrahedral Voids

Close-packed structures, such as CCP (cubic close-packed) or FCC (face-centered cubic), contain tetrahedral and octahedral voids.
In a unit cell of a CCP/FCC lattice, it is divided into eight smaller cubes.
Each small cube has atoms positioned at alternate corners, totaling 4 atoms per cube.
The arrangement of these atoms forms a regular tetrahedron.
Each small cube contains one tetrahedral void, resulting in eight tetrahedral voids in the entire unit cell.
The CCP structure has a total of 4 atoms per unit cell, leading to tetrahedral voids being twice the number of atoms, equaling eight tetrahedral voids.

Octahedral Voids

In the same unit cell of a CCP/FCC lattice, the body center remains unoccupied while being surrounded by six atoms located at the face centers.
Joins of these face centers create an octahedron, designating one octahedral void at the body center.
Additional octahedral voids exist at the center of each of the 12 edges of the cube.
These edge-centered octahedral voids are surrounded by a total of six atoms: four from the same unit cell and two from adjacent unit cells.
Each edge of the cube shares its octahedral void with four neighboring unit cells, meaning only one-fourth of each edge-centered void is attributed to any given unit cell.

Description

Explore the fascinating world of close-packed structures in this quiz focusing on locating tetrahedral and octahedral voids. Learn how a ccp or fcc structure is organized and the significance of these voids within the unit cell. Test your knowledge of unit cells and their configurations.