We may consider a crystal as a collection of identical unit cells. For a substance containing more than 1 kind of atom, the ratio of atoms in the unit cell must be exactly the same as in the entire crystal.

For example, the unit cell H3 contains 1 pink and (6 x 1/3 = 2) purple circles, or a ratio of 1:2.
          H3 unit cell                                                H3 lattice

The full lattice must also have a 1:2 ratio. Because the drawing does not end at the edges of the unit cells, the ratio you see (10:30) is not representative.

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  Structure of Crystals
Crystal Lattices
Unit Cells
From Unit Cell to Lattice
From Lattice to Unit Cell
Packing & Geometry
Simple Cubic Metals
Close Packed Structures
Body Centered Cubic
Cesium Chloride
Sodium Chloride
Rhenium Oxide
Niobium Oxide
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