Square antiprism

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Uniform Square antiprism
Square antiprism
Type Prismatic uniform polyhedron
Elements F = 10, E = 16
V = 8 (χ = 2)
Faces by sides 8{3}+2{4}
Schläfli symbol s{2,8}
sr{2,4}
Wythoff symbol | 2 2 4
Coxeter-Dynkin CDel node h.pngCDel 2x.pngCDel node h.pngCDel 8.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 4.pngCDel node h.png
Symmetry group D4d, [2+,8], (2*4), order 16
Rotation group D4, [4,2]+, (442), order 8
References U77(b)
Dual Tetragonal trapezohedron
Properties convex
Square antiprism
Vertex figure
3.3.3.4

In geometry, the square antiprism is the second in an infinite set of antiprisms formed by an even-numbered sequence of triangle sides closed by two polygon caps. It is also known as an anticube.[1]

If all its faces are regular, it is a semiregular polyhedron or uniform polyhedron.

When eight points are distributed on the surface of a sphere with the aim of maximising the distance between them in some sense, then the resulting shape corresponds to a square anti-prism rather than a cube. Different examples include maximising the distance to the nearest point, or minimising the sum of all reciprocals of squares of distances.

Molecules with square antiprismatic geometry[edit]

Square antiprismatic molecular geometry

According to the VSEPR theory of molecular geometry in chemistry, which is based on the general principle of maximizing the distances between points, a square antiprism is the favoured geometry when eight pairs of electrons surround a central atom. One molecule with this geometry is the octafluoroxenate(VI) ion (XeF82-) in the salt nitrosonium octafluoroxenate(VI); however, the molecule is distorted away from the idealized square antiprism.[2]

In addition, the element sulfur forms octatomic S8 molecules as its most stable allotrope. The S8 molecule has a structure based on the square antiprism, in which the eight atoms occupy the eight vertices of the antiprism, and the eight triangle-triangle edges of the antiprism correspond to single covalent bonds between sulfur atoms.

In architecture[edit]

One World Trade Center

The main building block of the One World Trade Center (at the site of the old World Trade Center destroyed on September 11, 2001) has the shape of an extremely tall square antiprism.

Related polyhedra[edit]

As an antiprism, the square antiprism belongs to a family of polyhedra that includes the octahedron (which can be seen as a triangle-capped antiprism), the pentagonal antiprism, the hexagonal antiprism, and the octagonal antiprism.

The gyroelongated square pyramid is a Johnson solid (specifically, J10) constructed by replacing one square of a square antiprism with a square pyramid. Similarly, the gyroelongated square bipyramid (J17) is a deltahedron (a polyhedron whose faces are all equilateral triangles) constructed by replacing both squares of a square antiprism with a square pyramid.

The snub disphenoid (J84) is another deltahedron, constructed by replacing the two squares of a square antiprism by pairs of equilateral triangles. The snub square antiprism (J85) can be seen as a square antiprism with a chain of equilateral triangles inserted around the middle. The sphenocorona (J86) and the sphenomegacorona (J88) are other Johnson solids that, like the square antiprism, consist of two squares and an even number of equilateral triangles.

The square antiprism is first in a series of snub polyhedra and tilings with vertex figure 3.3.4.3.n.

Dimensional family of snub polyhedra and tilings: 3.3.4.3.n
Symmetry
4n2
[n,4]+
Spherical Euclidean Compact hyperbolic Paracompact
242
[2,4]+
342
[3,4]+
442
[4,4]+
542
[5,4]+
642
[6,4]+
742
[7,4]+
842
[8,4]+...
∞42
[∞,4]+
Snub
figure
Spherical square antiprism.png
3.3.4.3.2
Spherical snub cube.png
3.3.4.3.3
Uniform tiling 44-snub.png
3.3.4.3.4
Uniform tiling 54-snub.png
3.3.4.3.5
Uniform tiling 64-snub.png
3.3.4.3.6
Uniform tiling 74-snub.png
3.3.4.3.7
Uniform tiling 84-snub.png
3.3.4.3.8
Uniform tiling i42-snub.png
3.3.4.3.∞
Coxeter
Schläfli
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{2,4}
CDel node h.pngCDel 3.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{3,4}
CDel node h.pngCDel 4.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{4,4}
CDel node h.pngCDel 5.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{5,4}
CDel node h.pngCDel 6.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{6,4}
CDel node h.pngCDel 7.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{7,4}
CDel node h.pngCDel 8.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{8,4}
CDel node h.pngCDel infin.pngCDel node h.pngCDel 4.pngCDel node h.png
sr{∞,4}
Snub
dual
figure
Spherical tetragonal trapezohedron.png
V3.3.4.3.2
Spherical pentagonal icositetrahedron.png
V3.3.4.3.3
Tiling Dual Semiregular V3-3-4-3-4 Cairo Pentagonal.svg
V3.3.4.3.4
Order-5-4 floret pentagonal tiling.png
V3.3.4.3.5
V3.3.4.3.6 V3.3.4.3.7 V3.3.4.3.8 V3.3.4.3.∞
Coxeter CDel node fh.pngCDel 2x.pngCDel node fh.pngCDel 4.pngCDel node fh.png CDel node fh.pngCDel 3.pngCDel node fh.pngCDel 4.pngCDel node fh.png CDel node fh.pngCDel 4.pngCDel node fh.pngCDel 4.pngCDel node fh.png CDel node fh.pngCDel 5.pngCDel node fh.pngCDel 4.pngCDel node fh.png CDel node fh.pngCDel 6.pngCDel node fh.pngCDel 4.pngCDel node fh.png CDel node fh.pngCDel 7.pngCDel node fh.pngCDel 4.pngCDel node fh.png CDel node fh.pngCDel 8.pngCDel node fh.pngCDel 4.pngCDel node fh.png CDel node fh.pngCDel infin.pngCDel node fh.pngCDel 4.pngCDel node fh.png

The square antiprism can be truncated and alternated to form a snub antiprism:

Snub antiprisms
Antiprism Truncated
t
Alternated
ht
Square antiprism.png
s{2,8}
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 8.pngCDel node.png
Truncated square antiprism.png
ts{2,8}
Snub square antiprism colored.png
ss{2,8}

See also[edit]

Family of uniform antiprisms
2 3 4 5 6 7 8 9 10 11 12 n
s{2,4}
sr{2,2}
s{2,6}
sr{2,3}
s{2,8}
sr{2,4}
s{2,10}
sr{2,5}
s{2,12}
sr{2,6}
s{2,14}
sr{2,7}
s{2,16}
sr{2,8}
s{2,18}
sr{2,9}
s{2,20}
sr{2,10}
s{2,22}
sr{2,11}
s{2,24}
sr{2,12}
s{2,2n}
sr{2,n}
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 4.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 2x.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 6.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 3.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 8.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 4.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 1x.pngCDel 0x.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 5.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 1x.pngCDel 2x.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 6.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 1x.pngCDel 4.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 7.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 1x.pngCDel 6.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 8.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 1x.pngCDel 8.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 9.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 2x.pngCDel 0x.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 10.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 2x.pngCDel 2x.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 11.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 2x.pngCDel 4.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 12.pngCDel node h.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel 2x.pngCDel n.pngCDel node.png
CDel node h.pngCDel 2x.pngCDel node h.pngCDel n.pngCDel node h.png
Digonal antiprism.png Trigonal antiprism.png Square antiprism.png Pentagonal antiprism.png Hexagonal antiprism.png Antiprism 7.png Octagonal antiprism.png Enneagonal antiprism.png Decagonal antiprism.png Hendecagonal antiprism.png Dodecagonal antiprism.png
As spherical polyhedra
Spherical digonal antiprism.png Spherical trigonal antiprism.png Spherical square antiprism.png Spherical pentagonal antiprism.png Spherical hexagonal antiprism.png Spherical heptagonal antiprism.png Spherical octagonal antiprism.png

Notes[edit]

  1. ^ Holleman-Wiberg. Inorganic Chemistry, Academic Press, Italy, p. 299. ISBN 0-12-352651-5.
  2. ^ Peterson, W.; Holloway, H.; Coyle, A.; Williams, M. (Sep 1971). "Antiprismatic Coordination about Xenon: the Structure of Nitrosonium Octafluoroxenate(VI)". Science 173 (4003): 1238–1239. Bibcode:1971Sci...173.1238P. doi:10.1126/science.173.4003.1238. ISSN 0036-8075. PMID 17775218.  edit

External links[edit]