Question

Name the two types of void space in close packing.

Answer 1

There are two types of interstitial voids in a 3D structure:

1. Tetrahedral voids: In cubic close packed structure, spheres of the second layer lie above the triangular voids of the first layer. Each sphere touches the three spheres of the first layer. By joining the centre of these four spheres, it forms a tetrahedron and the empty space left over by joining the centre of these spheres forms a tetrahedral void.

In closed packed structure the number of tetrahedral voids is two times the number of spheres.

Let the number of spheres be n.

Then the number of tetrahedral voids will be 2n.

2. Octahedral voids: Adjacent to tetrahedral voids you can find octahedral voids. So now, what are Octahedral Voids? When the triangular voids of the first layer coincides with the triangular voids of the layer above or below it, we get a void that is formed by enclosing six spheres. This vacant space formed by combining the triangular voids of the first layer and that of the second layer are called Octahedral Voids.

If the number of spheres in a close-packed structure is n, then the number of octahedral voids will be n.