**NaCl**** **

__Stoichiometry__ = AX

__Space Group__ = Fm3m (225)

__Atomic Positions__

A 4a
0, 0, 0

X 4b
½, ½, ½

__Coordination Numbers/Geometry__

A CN=6
Octahedral coordination

X CN=6
Octahedral coordination

__Representative Compounds__*

Intermetallics (55) -
(i.e. PY)

Oxides (22) - (i.e.
MgO)

Halides (21) - (i.e.
LiF)

Carbides (10) - (i.e.
ZrC)

Borides (3) - (ZrB,
PuB, HfB)

Hydrides (5) - (i.e.
PdH)

Nitrides (25) - (i.e.
ZrN)

Sulfides, Selenides
and Tellurides (63) - (i.e. SrS)

*The numbers in parentheses are
the number of compounds of each type found in "Structure and
Properties of Inorganic Solids" by Francis Galasso,
Pergammon Press (1970).

__Description__**
**

The rock salt structure is a highly symmetric one that can be
described in many different ways:

(1) The structure can be generated by putting both Na and Cl on the same sites in a FCC lattice, then shift one of the two networks (Na or Cl) by (½, 0, 0).

(2) The structure can also be described as a cubic close packing of anions, with all of the octahedral holes filled by cations (or vice versa). This description can clearly be seen in the left hand figure above.

(3) From a polyhedral
representation the NaCl_{6} octahedra are seen to share
all 8 edges with neighboring octahedra, as seen in the right hand
figure above.

The high symmetry and efficient packing of this structure is favored by a wide variety of materials including:

- ionic compounds with AX stoichiometry (i.e. MgO, NaCl),
- metallic nitrides and carbides (i.e. ZrN, NbC)
- ordered intermetallics containing As, Bi, Sb, and P (i.e. AsSc, BiLa, HoSb, PZr)

The pyrite, FeS_{2} (fools
gold) and CaC_{2} structures are derived from the NaCl
structure by substituting linear S_{2} and C_{2}
units respectively onto the chloride lattice sites. Orientation
of the S_{2} and C_{2} units is different
however, giving rise to different space groups for each (FeS_{2}
= Pa3, CaC_{2} = I4/mmm).