Crystal structures of halides

NaCl, CsCl, CaF₂, and ZnS
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1. Sodium chloride, NaCl

Push button for spacefilling model of NaCl

Push to go back to ball-and-stick model

Push to show face-centered cubic arrangement of Na⁺ ions (blue)

Push to show face-centered cubic arrangement of Cl^– ions (green)

Highlight one Na⁺ ion and the octahedron of six Cl^– ions surrounding it

Highlight one Cl^– ion and the octahedron of six Na⁺ ions surrounding it

2. Cesium chloride, CsCl

Push for spacefilling

Push for ball-and-stick

Push to show simple cubic arrangement of Cs⁺ ions (pink)

Push to show simple cubic arrangement of Cl^– ions (green)

Highlight one Cs⁺ ion and the cube of eight Cl^– ions surrounding it

Highlight one Cl^– ion and the cube of eight Cs⁺ ions surrounding it

3. Calcium fluoride (fluorite, CaF₂), in two different views

(a) Centered on the Ca²⁺ ions

Push for spacefill (note that there are some Ca²⁺ ions "missing", i.e. not every cube of F^– ions has a Ca²⁺ ion in it)
Push for ball-and-stick
Highlight one Ca²⁺ ion and the cube of eight F^– ions surrounding it
Highlight one F^– ion and the tetrahedron of four Ca²⁺ ions surrounding it (b) Centered on the F^– ions

Push for spacefill
Push for ball-and-stick
Highlight one F^– ion and the tetrahedron of four Ca²⁺ ions surrounding it
Highlight a cube of eight F^– ions that contains no Ca²⁺ ion in the center!

4. and 5. Two different structures for zinc sulfide (ZnS)

4. Cubic structure (sphalerite)

Push for spacefill (note that now half of the anions have been removed from the CaF₂ structure, so now both anions and cations have CN = 4)
Push for ball-and-stick
Highlight one Zn²⁺ ion and the tetrahedron of four S^2– ions surrounding it 5. Hexagonal structure (wurtzite)

Push for spacefill
Push for ball-and-stick
Highlight one Zn²⁺ ion and the tetrahedron of four S^2– ions surrounding it

6. NiAs (niccolite), a layer structure
In this structure there are alternating layers of Ni (blue) and As (pink) atoms. This leads to a lot of close Ni-Ni and As-As contacts, but that's OK because the crystal is highly covalent.
Push for spacefill
Push for ball-and-stick
Highlight one Ni atom and the octahedron of six As atoms surrounding it
Highlight one As atom and the trigonal prism (not an octahedron!) of six Ni atoms surrounding it

Thanks to Mike Mehl, of the Naval Research Laboratory, for the wurtzite and NiAs coordinates.