Build SC, BCC, FCC and HCP unit cells in 3D, count atoms per cell, see tetrahedral and octahedral voids, and calculate density.
Last updated: 26 October 2026
Set sphere size to 100% to see where atoms touch: along the edge (SC), the body diagonal (BCC) or the face diagonal (FCC). Turn on voids to see where small ions fit. Syllabus note: unit cells and crystal structures are not a unit in the current JEE Main chemistry topic list on this site. They still appear in older PYQs and some other exams, so check the latest official syllabus before spending time here.
Drag to rotate, two fingers or right-drag to pan, scroll or pinch to zoom. The toolbar has views, cutaway, measure and “show the maths”.
Four: 8 corners × 1/8 + 6 face centres × 1/2 = 4.
68%. Atoms touch along the body diagonal, so √3·a = 4r.
If there are N atoms, there are N octahedral voids and 2N tetrahedral voids. An FCC cell has 4 octahedral and 8 tetrahedral voids.
