CHM 3301 Laboratory Report
UNIVERSITI PUTRA MALAYSIA FACULTY OF SCIENCE CHEMISTRY DEPARTMENT
CHM 3301 INORGANIC CHEMISTRY I LABORATORY REPORT 2011/2012
EXPERIMENT NUMBER
:2
TITL TITLE E OF OF EXPE EXPERI RIME MENT NT
: THE THE STR STRUC UCTU TURE RE OF SOLI SOLIDS DS
NAME
: MUHAMMAD NOORHADI BIN AHMAD
MATRIC NUMBER
: 159057
PROGRAMME TA TAKEN
: B. B.Sc(K) CH CHEMISTRY
PARTNER’S NAME
: MUHD FUAD BIN MOHD FODZIK
MATRIC NUMBER
: 158338
PROGRAMME TA TAKEN
: B. B.Sc(K) CH CHEMISTRY
LECTURER’S NAME
: DR. TAN KAR BAN
DEMONSTRATOR DEMONSTRATOR’S ’S NAME : SITI HUSNAA BTE MOHD MOHD TALIB SUBMISSION DATE
: 18/10/2011
CHM 3301 Laboratory Report Experiment 2: The structure of solids Objectives: By the end of this experiment, student should be able to 1. Explore how atoms, ions, or molecules in simple solids are arranged. 2. Build crystal structures using Ping-Pong balls. The atoms are represented by spheres and the solid is the outcome of stacking the spheres together densely, close-packed arrangement.
Introduction Crystal is a product from the arrangement of atoms, molecules or ions in the process called crystallization. The atoms, ions or molecules involved in crystallization are the repeating units in a solid, so called the unit cell. A unit cell builds a solid by arranging them into rows and stacks. In the process of arranging them into a solid, the outcome might be simple cubic packing, body-centered cubic packing, hexagonal closest-packed structure and cubic closestpacked structure. All these kind of structures will be discussed throughout the experiment. Simple cubic packing can be illustrated in a cube where the particles are arranged in straight, and the layers are neat. The layers are identical, in which the layer are oriented directly onto the lower layer. This means that the arrangement are just top and bottom of each layer and the spaces between then are left behind. The spaces leave were very large and about 52% of the available space is actually by the spheres, making insufficient use of sphere and minimizing attractive forces between the spheres. Body centered cubic packing is another concept, it separate the sphere to form a square-packed plane in which they do not quite each other. In their arrangement, the layers are linear and more organized. The arrangement is more compact and each layer is off-set from the above layer. The spheres in the second plane pack above the holes in the first plane. Then, the spheres in the third plane pack above the holes in the second plane. Sphere in the fourth plane pack above the third plane, and so on. As the spaces used are much higher compare to the simple cubic packing thus, about 68% of the available spaces are quite efficient for this solid. Now we move on to the closest packed which is hexagonal closest-packed and cubic closest packed structure. Hexagonal closest-packed (HCP) has its own arranging system in which the style is ABABAB, the type of stacking of close packing layers. This kind of pattern gives the lattice with a hexagonal unit cell. Besides that, the smallest lattice repeat is called primitive hexagonal unit cell. This is one of the most efficient methods of packing spheres in which almost 74% of the hexagonal closest packed structures are filled.
CHM 3301 Laboratory Report Cubic closest packed structure is another way of stacking closest packed planes of sphere. In this lattice, the spheres of the third layer are placed above the holes in the first layer that were not used to form the second layer. The fourth layer of the spheres packs directly above the first. This result in an ABCABC…..pattern. Furthermore, the lattice is called cubic closest packed is because it has the smallest unit cell that can be called face-centered cubic. Since the lattice is cubic closest packing, it can pack the space up to 74% as it efficient in its packaging as hexagonal closest packed structures. There are two kinds of interstitials or holes (or unoccupied space) in a closest-packed structure. They are an octahedral hole and a tetrahedral hole. An octahedral hole, the holes lies between two oppositely directed planar triangles of spheres in adjoining layers. There are N octahedral hole, for the N atoms in the crystal. The hole has local octahedral symmetry. Next, a tetrahedral hole, the hole is formed by a planar triangle of touching spheres that is capable by single spheres lying in the dip (hole) between them. The apex of the tetrahedron maybe directed up (T) or down (T’) in the crystal. There N tetrahedral holes of each type (2N in all). They are called tetrahedral holes because ions that pack in these holes are surrounded by four appositely charge ions arranged towards the corners of a tetrahedron. Now we continue with the structures of metals. The structures of pure metals can be thought of as identical perfects spheres. The same can be said about the rare gases at very low temperatures. These substances crystallize in one of the four basic structures: simple cubic, body centered cubic, hexagonal closest pack or cubic centered pack. Lastly is the ionic solid. Ionic solid can be derived from the arrays in which the anions or cations are stacked together in face centered cubic or hexagonal closest packed patterns and the counters ion occupy the octahedral and tetrahedral holes in the lattice. The closest packed layer usually needs to expand in order to accommodate the counters ions, but this is often a minor perturbation of the anion arrangement.
Practical Questions The packing of spheres in crystalline solids. By using the Ping-Pong balls given to you, assemble the four basic structures of packing of spheres as described in the theory. 1. Based on the models you made, draw (in 3-dimension) all the four types of packing arrangements. 2. Draw a unit cell for each packing arrangements.
CHM 3301 Laboratory Report 3. Determine the nearest neighbor of each sphere in simple cubic, body centered cubic, hexagonal closest pack and cubic centered pack structures and thus determine the coordination number. 4. Calculate the maximum radius of sphere that may be accommodated in an octahedral hole in a closest-packed solid, if the radius of a sphere is r, and that of the hole is r h. 5. Give examples of some metallic element that crystallize in simple cubic, body centered cubic, hexagonal closest pack or cubic centered pack structures. SC : NH4Cl , BCC : Fe , HCP : Ni
Ionic solids. Models of the following compounds are made available to you: CsCl , CsF , ZnS and CaF 2 1. Draw the structures of the ionic given. 2. What are the coordination numbers of the anion and cation in each structure? CsCl : (8 x 1/8) + (1/2 x 6) = 4 CsF : (12 x 1/4) + (1x1) = 4 ZnS : (8 x 1/8) + (1/2 x 6) = 4 CaF2 : (8 x 1/8) + (1/2 x 6) = 4 3. How many Cs + and Cl - ions are there in the CsCl unit cell? Cs+ ion : 8 , Cl- ions : 8 Therefore Cs:Cl = 8:8 = 1:1 4. How many Zn2+ and S2- ions are there in the sphalerite unit cell? Zn2+ ions : 4 , S2- ions : 4 Therefore, Zn:S = 4:4 = 1:1 5. CsF adopt NaCl structure but not CsCl. Why? CsCl has the primitive cubic lattice structure compare to CsF that have the cubic closed packed lattice structure. CsCl also has 8 coordination number while CsF has 12 coordination number.
CHM 3301 Laboratory Report 6. Distinguish the differences among the structures of CsCl, CsF and CaF 2? CsCl has simple cubic lattice structure. CsF has octahedral structure and CaF cubic central system.
2
has the
Covalent network solid – graphite and diamond structures. You are given model and graphite structures, representing covalent network solids. 1. Write a short note on the description of structure, bonding and geometry of diamond and graphite. Diamond is a face centered cubic lattice structure. It is bonded tetrahedrally to carbon atoms (sp3) into diamond lattice. Diamond is covalently bonded between its atoms. Graphite is arranged in hexagonal lattice and has planar structure. 2. Can you name other covalent network solids apart from diamond and graphite? Quartz Discussion. Every single solid have their shape. The shape may be simple cubic packing, bodycentered cubic packing, hexagonal closest-packed structure or cubic closest-packed structure. Before we look into details in each shape, let’s look what lattice, unit cell and primitive meant. Lattice is a 3-dimensional, infinite array of points, the lattice points, each of which is surrounded in an identical way by neighbouring points and which defines the basic repeating structure of the crystal. Unit cell of the crystal is an imaginary parallel-sided region or parallelepiped, from which the entire crystal can be built up by purely translational displacements, unit cells so generated fit perfectly together with no space excluded. A primitive unit cell has just one lattice cell in the unit cell and the translational symmetry present is just that on the repeating unit cell. Coordination number is the total number of attachment at the central element. It can be varies from 2 to 6 but commonly the coordination number is 6. Coordination number is also depends on several factors such as the size of the metal ion and ligand, the type of bonding and also by the electronic configuration of the metal ion. For details, it can be seen that the bigger the charge on the central ion, the higher the attraction for negatively charged ligands, however, the bigger the charge of the smaller ion, the lesser the number of groups able to coordinate. Coordination for each lattice is differing from each structure. For example, simple cubic, the coordination is 6. This is because it is not close packed solid and also primitive with atoms at the corner. The unit cell is 1. The atoms are in contacted at the cell edge. This arrangement is very rare and one example of it is form of Polonium. Next, body centered cubic has the coordination of 8. The unit cell for body centered cubic is 2. Then, hexagonal closest packed
CHM 3301 Laboratory Report coordination number is 12, and the unit cell is 4 (8 at the corner: 1/8 x 8 = 1, 6 in the faces: 1/2 x 6 = 3). Lastly, cubic closest packing coordination number is 12, and the unit cell is 4 (8 at the corner: 1/8 x 8 = 1, 6 in the faces: 1/2 x 6 = 3). Now we will discuss on the type of bonding that make the lattice has the arrangement that we can see throughout the experiment is being conducted. The type of bonding that holds each lattice is metallic bonding and ionic bonding. Metallic bonding is a kind of bonding that bind metals when each atoms loses one or more electrons to the electron sea. The strength of the binding results from the combined attractions between all these freely moving electrons and the resulting cation. Some characteristics of metallic bonding are having low ionization energy. Besides that, ionic bond is a type of bond that through electrostatic attraction which is held together in rigid, symmetrically array as a result of the attraction between opposite charges. Ionic bonding depends on the electron loss and gain.
Conclusion. 1. Every molecule has its own structure, orientation, and characteristic. 2. Diamond and graphite can be determined its characteristic, which is hexagonal closest packed. 3. Coordination number and unit cell of a lattice can be determined by a formula. 4. The type of bonding involve in lattice is ionic bond and metallic bonding.
References. 1. D.F. Shriver and P.W. Atkin, Inorganic Chemistry, 3 rd Edition, 1999. Oxford University Press. 2. G.L. Miessler and D.A Tarr, Inorganic Chemistry, 3 rd edition, 2004, Pearson Prentice Hall. 3. http://www.kings.edu/chem.purdue/genchem/topicview/bp/ch13/structure.hhtm 4. http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Coordination_Chemistry/Coordination_ Numbers 5. http://www.tulane.edu/~sanelson/eens211/paulingsrules.htm 6. http://info.lu.farmingdale.edu/depts/met/met205/lattice.html 7. http://cst-www.nrl.navy.mil/lattice/
CHM 3301 Laboratory Report
