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Structure World

The Sodium Chloride Structure

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General Notes

NaCl has a cubic unit cell. It is best thought of as a face-centered cubic array of anions with an interpenetrating fcc cation lattice (or vice-versa). The cell looks the same whether you start with anions or cations on the corners. Each ion is 6-coordinate and has a local octahedral geometry.

Structural Information

NaCl Vital Statistics
Formula NaCl
Cystal System Cubic
Lattice Type Face-Centered
Space Group Fm3m, No. 225
Cell Parameters a = 5.6402 Å, Z=4
Atomic Positions Cl: 0, 0, 0   Na: 0.5, 0.5, 0.5
(can interchange if desired)
Density 2.17
Melting Point 804 degrees C
Alternate Names Halite, rock salt, sea salt,
table salt, salt
Isostructural
Compounds
MgO, TiO, TiC, LaN, NaI
KCl, RbF, AgCl, SrS

Structure

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Fig. 1 A single unit cell of NaCl Fig. 2 A 3x3x3 lattice of NaCl

Shown below are two crystallographic planes in NaCl. Notice that the (111) plane is hexagonally closest packed.

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Fig. 3 The (111) plane of NaCl. Fig. 4 The (100 plane of NaCl.

Something that surprises novices is that the 111 plane does not contain the body centered atom. It is important for the beginning student to recognize that the 111 plane does not cut through 1/2, 1/2, 1/2! Take a look at the models above and below to convinvce yourself of this very important fact!

Here is a polyhedral representation of the NaCl unit cell. We could have drawn octahedra around either of the two atoms. In the case below, we have drawn them around the corner atoms and changed the color to improve the image contrast:

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Chime models

Shown here is a Chime model you can rotate and manipulate. Notice that you can see alternating hcp layers that contain only Na and only Cl atoms if you manipulate it correctly. See the drawing of the 100 plane shown above if this orientation is not clear.

Fig. 5 A single unit cell of NaCl. Fig. 6 Bigger NaCl chunk coming soon.

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This page was last updated Monday, March 30, 2015
This document and associated figures are copyright 1996-2015 by Rob Toreki. All rights reserved.