In a hexagonal close-packed (hcp) arrangement of atoms, the unit cell consists of three layers of atoms. The top and bottom layers (a) contain six atoms at the corners of a hexagon and one atom at the center of each hexagon. The middle layer (b) contains three atoms nestled between the atoms of the top and bottom layers, hence, the name close-packed. The hexagonal close packed structure can be made by piling layers in the a-b-a-b-a-b... sequence.
Close packing is the packing of spheres so as to occupy the minimum amount of space. The name close packed refers to the packing efficiency of 74.05 %. There are two types of close packing: hexagonal and cubic. One layer, with atoms centered on sites labeled a. Two layers, with the atoms of the second layer centered on sites labeled b. The third layer can be placed on the sites labeled c (giving cubic close-packing) or over those marked a (giving hexagonal close-packing).
In a cubic close-packed (ccp) arrangement of atoms, the unit cell consists of four layers of atoms. The top and bottom layers (a) contain six atoms at the corners of a hexagon and one atom at the center of each hexagon. The atoms in the second layer (b) fit into depressions in the first layer. The atoms in the third layer (c) occupy a different set of depressions than those in the first. The cubic close packed structure can be made by piling layers in the a-b-c-a-b-c-a-b-c... sequence.
Primary structure of proteins is a sequence of defined amino acids in some protein.
Hexagonal crystal system is based on four crystallographic axes. The system of crystallographic axes of the hexagonal crystal system consists of three equivalent horizontal (equatorial) axes of which the positive ends make an angle of 120°. These axes are sometimes denoted as a, b and d axes. The fourth axis is (c) is perpendicular to and shorter or longer than the other three.
Hexagonal lattice has lattice points at the twelve corners of the hexagonal prism and at the centers of the two hexagonal faces of the unit cell. It has unit cell vectors a=b≠c and interaxial angles α=β=90° and γ=120°.
Lewis structure is the representation of the electron arrangement in atoms, ions, or molecules by showing the valence electrons as dots placed around the symbols for the elements.
Planary structure of molecule is a structure of molecule in which all atoms in the molecule lie in the same plane.
The ringlike structure is a structure by which the cycloalcanes and aromates are shown.
Generalic, Eni. "Hexagonal close-packed structure." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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