![]() ![]() ![]() That is total number of sodium and chlorine ions per unit cell are 8.Įach Na+ and 6 Cl- ions as nearest neighbors and similarly each Cl- ion has 6 Na+ ions has nearest neighbours. Thus, there are 4 Na+ and 4Cl- ions per unit cell. Therefore total number of chlorine ions per unit cell = 1+3 = 4 ions. Number of face centered Cl – ions per unit cell There are 8 chlorine atoms in the corners and they are shared by 8 adjacent unit cells.Įach face centered Cl – ion is shared by 2 adjoining unit cell. Here, there are two types of Cl – ion namely Corner Cl ion and face centered Cl ion as shown in the figure. Therefore, the number of sodium ions per unit cell = 3+1=4 ions One sodium ion is located at the center of the unit cell. Number of mid point Na+ ions per unit cell Each sodium ion is shared by 4 adfacent unit cell. ![]() Na+ ion is located at the midpoint of the axial length. Let us find the number of sodium ions separately. In NaCl structure, it has two types of ions namely, Na + and Cl – . Let us discuss the important parameters of the NaCl crystal. When one of the Cl ions has the origin at (0,0,0) then one of the nearest Thus NaCl crystal can be thought of as a compound of two FCC Na+ and Na + ions are situated exactly at the middle of the axial length of the unit cell along each axis. The Cl – ions are situated at the corners as well as at the centers of the faces of the cube. NaCl crystal has FCC structure with Na+ ion and cl ion as shown in the figure. Sodium choride and many other ionic crystals crystalline in rock slat structure which is also known as sodium chloride structure. Genrally, the cations (+ ve) are smaller in size to anions. Ionic solids are made up of cat ion(+ion) and anions (-ion). Since the packing density is very low, it is termed as very loosely packed structure. Thus we can say that 34% voulme of the unit cel in diamond cubic structure is occupied by the atoms and the remaining 66% volume is vacant. Substituting equations(2) and (3) in (1) we get Volume occupied by the atoms per unit cell (v)/volume of the unit cell(V) - > (1) Therefore the coordination number of diamond is 4 We know that the coordination number is the nearest atoms (shown by double line) for Y atom is 4. Let us draw perpendicular to the Y atom, which meets the unit cell at a point’Z’ as shown in the figure, which is a distance of a/4. But both the face centered atoms and the corner atoms have contact with the 4 atoms (1,2,3,4)įrom figure, we can see that the nearest two neighbors which have direct contact (shown by double line) are atoms’X’ and’Y’. Here, the corner atoms do not have contact with each other and the face centered atoms also do not have contact with the corner atoms. We know atomic radius is defined as half the distance between any two nearest neighbor atoms, which have direct contact with each other. Total number of atoms per unit cell = 1+3+4=8 Inside the unit cell we have 4 atoms, represented by 1,2,3,4 in the figure which is shared by that particular unit cell alone. The number of face centered atom per unit cell = ½ x 6 = 3 atoms Similarly, we have 6 face centered atoms. Number of face centered atoms per unit cellĮach face centered atom is shared by 2 unit cells.The number of corner atoms in an unit cell. Similarly we have 8 corner atoms in an unit cell. The three type of atoms positions projected on a cube face is as shown.Įach corner atom is shared by 8 unit cells.Four atoms present inside the unit cell an s represented as 1, 2.3,4 as shown in the figure.Face centered atoms, represented by ‘F’ as shown in the figure.Corner atoms, represented by ‘F’ as shown in the figure.Let us now discuss some of the important parameters of the diamond Thus from the figure we can see that diamond structure is formed due to the combination of two interpenetrating FCC sub lattices, having the origin (0,0,0) and (1/4,1/4,1/4) along the body diagonal. The ‘X’ atom is located with an origin (0, 0, 0) and the Y atom is located with an orgin of (a/4, a/4, a/4) (i.e) one quarter of the way along the body diagonal as shown in the figure: Diamond has face centered structure (FCC) with the basis of two carbon atoms viz., ‘X’ and ‘Y’. ![]()
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