Close Packing Three Dimensions

Introduction

Closed (closet) packing is defined or understood as the arrangement of atoms, ions, or molecules present in the crystal lattice that is characterized by the largest (greatest) number of atoms present in the per unit volume (V) of the crystal. Close (closet) packing is expressed (distinctly) in a large number of crystal structures. Also, it is an important characteristic of most metals and some crystallized inert gases.

All the particles (may be atoms, ions, or molecules) to be combined in the formation of the crystal lattice must have the same (similar or equal) spherical solid shape. There are various forms of close packing one-dimensional (1-D) close packing, two-dimensional (2-D) close packing, and three-dimensional (3-D) close packing. Hexagonal close packing is formed when a sphere shares its surface (in contact) with the other six (surrounded) spheres. This type of packing is also known as the ABABA… type arrangement in 2-D.

There are many crystals or crystal structures that are based (dependent) on a close-packing of similar or single kinds of atoms, also there are close (closet) packing of large ions with the filling of smaller ions between the spaces left over there. There are various (different) forms of close packing like one-dimensional (1-D) close packing, two-dimensional (2-D) close packing, and three-dimensional (3-D) close packing. Hexagonal close packing (HCP) is formed when a sphere shares its surface (in contact) with the other six (surrounded) spheres. This type (manner) of packing is also known as the ABABA… type arrangement in 2-D.

Cdang Derivative work: Muskid, Closepacking, CC BY-SA 3.0

Hexagonal Closest Packing

Three (3) layers of atoms make up the unit cell in a two-dimensional arrangement of atoms known as hexagonal tight packing. Six (6) atoms are located at each hexagon's corners (or edges) in the top (above) and bottom (below) layers, and each hexagon also has one atom in its middle. The intermediate layer is called close-packed because it is composed of three (3) atoms that are sandwiched between those the top and bottom layers. One of the two (2) simple (easily) ways of packing atoms with the highest (most) density in this form of tight packing; the other is a face-centred cubic lattice (fcc). Some of the metals containing or having HCP-type structures are - magnesium (Mg), zinc (Zn), cobalt (Co), cadmium (Cd), e.t.c. But the ductile property of HCP metals is quite low as compared to FCC metals.

User:Greg L, Hexagonal close-packed unit cell, CC BY-SA 3.0

Cubic Closest Packing

Atoms can also be arranged in a 2-Dimensional structure called cubic closed (closet) packing. In this instance, the unit cell is made up of four (4) layers of atoms. Six (6) atoms are located at each hexagon's corners (or edges) in the top (above) and bottom (below) layers, while one (1) atom is located in the middle of each hexagon. The compression in the first (1st) layer can accommodate the atoms in the second (2nd) layer. Additionally, compared to the atoms in the first layer, those in the third layer (third) occupy a different (unique) set of compressions. There are three distinct types of cubic lattices based on cubic close packing: simple cubic lattice, face-centred cubic lattice, and body-centred cubic lattice. Some examples of cubic close (closet) packing are- copper (Cu), silver (Ag), nickel (Ni), and aluminium (Al).

Tomruen, Square circle grid spheres, CC BY-SA 4.0

Close Packing in Crystals

In crystals (during their formation) the constituent particles (may be atoms, molecules, or ions) are closely interlinked with one another. A tightly (densely) packed arrangement is one in which the maximum (highest) available space (region) is occupied (filled) by leaving the minimum (least) free space.

This corresponds (relates) to the condition (requirement) of the maximum or highest possible density (d). And, the stability of the closed system is directly proportional to the packing condition, that is closer (nearer) the packing, the higher (greater) the stability of the packed system. Most of the solids (s) we come to know about or visible to us are crystal solids. As we know the shape and sizes of the constituent particles present in a crystal are (maybe) different (unique), so the method of closed or closet packing of the particles (a constituent) will also vary (changes) according to the shape and sizes of the lattice. Here, the arrangement of the spheres should be much more effective so that the empty spaces will be the least or minimum.

Conclusion

Any kind (form) of crystal or crystal lattice is formed (generated) from various constituent particles of different (distinct) shapes or sizes and that’s why the method (process) of the closet (closed) packing of the particles (a constituent) also varies (changes) according to their shape and size. Closed packing or closet packing is defined (referred) as the arrangement (efficiently) of the constituent particles present in the crystal lattice (crystals). For all the particles (may be atoms, ions, or molecules) to be joined in the formation of the crystal lattice must have the same (similar or equal) spherical solid (s) shape. Hexagonal close packing is formed when a sphere shares its surface (in contact) with the other six (surrounded) spheres. This type of packing is also known as the ABABA… type arrangement in 2-D.

FAQs

1. What is the closed packing of atoms?

Closed (closet) packing is defined or understood as the arrangement of atoms, ions, or molecules present in the crystal lattice that is characterized by the largest (greatest) number of atoms present in the per unit volume (V) of the crystal. Close (closet) packing is expressed (distinctly) in a large number of crystal structures.

2. What do you mean by primitive unit cells?

Primitive unit cells are those or types of unit cells (constituent particles) that are only found at the corners (edges) of the lattice.

3. What are the various forms of close packing?

Broadly, there are three forms or types of close packing and those are- one-dimensional (1-D) close packing, two-dimensional (2-D) close packing, and three-dimensional (3-D) close packing.

4. What do you mean by HCP?

HCP, or hexagonal close packing, is a two-dimensional arrangement of atoms in which the unit cell has three layers of atoms. Six (6) atoms are located at each hexagon's corners (or edges) in the top (above) and bottom (below) layers, and each hexagon also has one atom in its middle.

5. NaCl (Sodium Chloride) has which type of crystal arrangement?

Sodium Chloride has a cubic closed packing (CCP) type crystal arrangement.