Pentagonal pyramid explained

Type:Pyramid
Johnson
Edges:10
Vertices:6
Symmetry:

C5v

Vertex Config:

5 x (32 x 5)+1 x 35

Angle:In Johnson solid:
Properties:convex,
elementary (Johnson solid)
Net:pentagonal pyramid flat.svg

In geometry, pentagonal pyramid is a pyramid with a pentagon base and five triangular faces, having a total of six faces. It is categorized as Johnson solid if all of the edges are equal in length, forming equilateral triangular faces and a regular pentagonal base. The pentagonal pyramid can be found in many polyhedrons, including their construction. It also occurs in stereochemistry in pentagonal pyramidal molecular geometry.

Properties

A pentagonal pyramid has six vertices, ten edges, and six faces. One of its faces is pentagon, a base of the pyramid; five others are triangles. Five of the edges make up the pentagon by connecting its five vertices, and the other five edges are known as the lateral edges of the pyramid, meeting at the sixth vertex called the apex. A pentagonal pyramid is said to be regular if its base is circumscribed in a circle that forms a regular pentagon, and it is said to be right if its altitude is erected perpendicularly to the base's center.

C5v

: the pyramid is left invariant by rotations of one, two, three, and four in five of a full turn around its axis of symmetry, the line connecting the apex to the center of the base. It is also mirror symmetric relative to any perpendicular plane passing through a bisector of the base. It can be represented as the wheel graph

W5

; more generally, a wheel graph

Wn

is the representation of the skeleton of a sided pyramid. It is self-dual, meaning its dual polyhedron is the pentagonal pyramid itself.

J2

, a convex polyhedron in which all of its faces are regular polygons. The dihedral angle between two adjacent triangular faces is approximately 138.19° and that between the triangular face and the base is 37.37°. It is elementary polyhedra, meaning it cannot be separated by a plane to create two small convex polyhedrons with regular faces. Given that

a

is the length of all edges of the pentagonal pyramid. A polyhedron's surface area is the sum of the areas of its faces. Therefore, the surface area of a pentagonal pyramid is the sum of the four triangles and one pentagon area. The volume of every pyramid equals one-third of the area of its base multiplied by its height. That is, the volume of a pentagonal pyramid is one-third of the product of the height and a pentagonal pyramid's area. In the case of Johnson solid with edge length

a

, its surface area

A

and volume

V

are: \begin A &= \frac\sqrt \approx 3.88554a^2, \\ V &= \frac a^3 \approx 0.30150a^3.\end

Applications

In polyhedron

Pentagonal pyramids can be found as components of many polyhedrons. Attaching its base to the pentagonal face of another polyhedron is an example of the construction process known as augmentation, and attaching it to prisms or antiprisms is known as elongation or gyroelongation, respectively. Examples polyhedrons are the pentakis dodecahedron is constructed from the dodecahedron by attaching the base of pentagonal pyramids onto each pentagonal face, small stellated dodecahedron is constructed from a regular dodecahedron stellated by pentagonal pyramids, and regular icosahedron constructed from a pentagonal antiprism by attaching two pentagonal pyramids onto its pentagonal bases.

J9

, gyroelongated pentagonal pyramid

J11

, pentagonal bipyramid

J13

, elongated pentagonal bipyramid

J16

, augmented dodecahedron

J58

, parabiaugmented dodecahedron

J59

, metabiaugmented dodecahedron

J60

, and triaugmented dodecahedron

J61

.[1] Relatedly, the removal of a pentagonal pyramid from polyhedra is an example known as diminishment; metabidiminished icosahedron

J62

and tridiminished icosahedron

J63

are the examples in which their constructions begin by removing pentagonal pyramids from a regular icosahedron.

Stereochemistry

In stereochemistry, an atom cluster can have a pentagonal pyramidal geometry. This molecule has a main-group element with one active lone pair, which can be described by a model that predicts the geometry of molecules known as VSEPR theory. An example of a molecule with this structure include nido-cage carbonate CB5H9.

References

External links

Notes and References

  1. , pp. 84 - 88. See Table 12.3, where

    Pn

    denotes the prism and

    An

    denotes the antiprism.

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