Pauling’s Rules
GLY 4200
Fall, 2012
1
Planar Packing
• Hexagonal array of spheres
2
Primitive Hexagonal Array
• A type of close packing
3
A-B Layers
• Closest-packing
4
Hexagonal Closest Packing
5
A-B-C Layers
• Another form of closest-packing
6
Cubic
Closest
Packing
7
Halite Structure
• A derivative of the
CCP structure
8
Beryl
• Beryl is Be3Al2Si6O18 - unit cell shown above
• The yellow Si tetrahedra are in the upper layer, the
green ones in the lower layer
• The purple tetrahedra contain Be
• The solitary blue atoms are Al, in 6-fold
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coordination with the adjacent tetrahedral oxygens
Corner Sharing
• Tetrahedra sharing one atom
10
Edge Sharing
• Two atoms shared
11
Face Sharing
• Three atoms shared
12
Linus
Pauling
1901-1994
• One of two people who have
been the recipient of two Nobel
Prizes, the prize for chemistry
in 1954 and the peace prize in
1960
• During his long life, he was
engaged in a broad range of
interests within the sciences
and, along with many of his
colleagues in the scientific
community, was actively
involved in the antinuclear
bomb movement after World
War II
• Photograph by Michael
13
Collopy
Rule 1
• A coordinated polyhedron of anions is
formed about each cation, the cationanion distance being determined by the
radius sum, and the coordination
number of the cation by the radius ratio
14
Rule 2
• Sometimes called “The electrostatic
valiancy principle”
• In a stable ionic structure, the valence
of each anion, with changed sign, is
exactly or nearly equal to the sum of
the strengths of the electrostatic bonds
to it from the adjacent cations
15
Rule 3
• The existence of edges, and particularly of
faces, common to two anion polyhedra in a
coordinated structure decreases its stability;
this effect is large for cations with high
valency and small coordination number,
and is especially large when the radius
ratio approaches the lower limit of stability
of the polyhedron
16
Rule 4
• In a crystal containing different
cations, those of high valency and
small coordination number tend not to
share polyhedron elements with each
other
17
Rule 5
• “The principle of parsimony”
• The number of essentially different
kinds of constituents in a crystal tends
to be small
18
Isostructural Minerals
• Clockwise from upper left – halite
(NaCl), Galena (PbS), Periclase
19
(MgO), and Sylvite KCl)