The Fascination of Crystals and Symmetry

Unit 5.4

by Frank Hoffmann & Michael Sartor

NaCl

− a simple-complicated structure

NaCl (Halite, Rock salt)

Space group

Crystal class

Crystal system

F m 3 m (# 225)

m 3 m

cubic

the sodium cations are surrounded by six

chloride anions, and vice versa

octahedral coordination spheres

CN = 6:6

Na+ Cl-

Lattice parameter

a = b = c = 5.625 Å

= 90 °, = 90 °, = 90 °

each ion type forms a fcc (sub-)lattice

NaCl (Halite, Rock salt) – Fragility

+ -

+-+ -

+-

+ -

+-

+

-+

-

+

-

-

+

+ -

+--

+

+ -

+-

-

+

+ -

+-forceCleavage

tendency of crystals to split along definite crystallographic planes

perfect along {001}

+ -

+ +

- -

electrostatic attraction

electrostatic repulsion

6.7 x 1.9 x 1.7 cm

NaCl (Halite, Rock salt) – the three viewing directions

F m 3 m (# 225)Space group

[001]4/m [111]

3

Full symbol F 4/m 3 2/m

[110]2/m

3D structure (Vesta)

reproduce this with the

NaCl (Halite, Rock salt) – International Tables

NaCl (Halite, Rock salt) – multiplicity of 192…

…

Positions

Na4Cl4

Add an atom at a general position in VESTA

NaCl (Halite, Rock salt) – simply beautiful..

Picture Credits

If not otherwise stated pictures, images, sketches, clip arts are • self-taken/self-drawn or• public domain

Rob Lavinsky, iRocks.com | CC-BY-SA-3.0 Dubravko Sorić SoraZG on Flickr | CC-BY-SA-2.0