Close packing in crystals describes how the constituent particles are arranged in a crystal lattice to maximise available space. We must assume that all particles (atoms, molecules, and ions) have the same spherical solid shape in order to better understand this packing.
Consequently, a lattice’s unit cell has a cubic shape. There will always be some vacant spots in the cell when we stack the spheres. The placement of these spheres must be extremely effective in order to reduce these empty gaps. To avoid any vacant spots, the spheres should be placed as closely as feasible together.
Close packing in crystal
Close packing in crystals refers to the effective arrangement of the lattice’s component particles. We must assume that all particles (atoms, molecules, and ions) have the same spherical solid shape in order to fully understand this packing. Consequently, the unit cell of a lattice has a cubic shape. When we stack the spheres, there will always be a few empty spaces in the cell. To reduce these empty spaces, the arrangement of these spheres must be extremely effective. The spheres should be placed as closely as possible to one another to prevent empty spots.
Close packing in one dimension
In order to pack in one dimension, spheres must be lined up in a row with their neighbouring atoms touching. The coordination number is defined as the quantity of nearest neighbours. For one-dimensional close packing, the coordination number is 2.
Square close packing
The second row can be packed closely so that it is directly beneath the first row. Because of this, if we refer to the first row as a “A” type row, the second row, which is set up exactly like the first, is likewise a “A” type row. In this arrangement, each sphere is in contact with four other spheres. It has a four-coordination number as a result. We observe that a square is created when the centres of the four closest spheres are connected. This kind of packing is referred to as square close packing in two dimensions in crystalline solids.
Hexagonal close packing
The second row’s spheres are organised in this configuration so that they can fit into the first row’s depression. Type B is shown for the second row. The third row is set up similarly to row (A), while the fourth row is set up similarly to row 2. The layout is shown as ABAB, for example.
Close packing in three dimension
By adding layers to a square pack and arranging the initial layer in a hexagonal close-pack configuration, three-dimensional packaging can be created.
Three-dimensional close packing from two-dimensional square close-packed layers: This form of three-dimensional packing arrangement can be obtained by restating the AAAA type of two-dimensional arrangement in three dimensions. Of all the metals in the periodic table, only polonium crystallises in a straightforward cubic shape.
Three dimensions of close packing: The spheres in the first layer (type A) in this arrangement are slightly spaced, and the second layer is made up of the spheres arranged in the depressions between the spheres in layer A. The first layer is repeated in the third. This configuration, ABABAB, is repeatedly repeated on the crystal.
Coordination number
In chemistry, transitional elements/metals—primarily the d-block elements—give rise to a huge variety of complex compounds in which metal atoms are connected to many anions (ionised molecules that are negatively charged) or neutral molecules. According to the terminology used today, such substances are coordination compounds. One of the most fundamental ideas in coordination compound chemistry is the coordination number. Ligands are molecules or charged ions that are joined to the central atom or ion of a coordination complex.
Coordinate compounds
A family of molecules known as complex compounds includes coordination compounds. This is because of how these molecules’ chemistry works. Coordination complexes can only be produced by transition metals. The high charge-to-mass ratio and the accessibility of d-orbitals are the reason for this.
Many biological materials have coordination complexes. Numerous other coordination molecules also have important functions in biological processes. The bodies produce and absorb a significant number of complicated substances during various physiological processes. For plants to engage in photosynthesis, chlorophyll is necessary. Magnesium and porphyrin combine to form this chlorophyll. Coordination complexes make up a large portion of the enzymes that catalyse biological reactions in our bodies.
Conclusion
The constituent particles of crystalline solids are arranged in a predictable and repeating pattern. The term “crystal lattice” refers to the diagrammatic depiction of three-dimensional groupings of constituent particles in a crystal, in which each particle is represented as a point in space. The atoms in a crystal lattice are packed so closely together that there is hardly any room between them.