Molecular Modeling

MOLECULAR MODELING 1. Objectives ? Predictthe shape of identified compounds ? Construct molecular models of identified compounds and ? Determine the molecular structure of identified compounds. 2. scheme Building models of molecules argon useful for visualizing how atoms argon connected in three-dimensional space called molecular geometry, which is best predicted by Valence-Shell Electron-Pair Repulsion (VSPER) surmise. The following are the sets of rules summarizing thsi theory ? Consider molecules and ions where two or more atoms are bonded to a central atom. The electron pairs in the valency shell of the central atom are off-key to lay as far apart as possible because electron pair repels one another. The shape of the molecule or ion is a result of the electron-pair repulsion. ? totally the valence-shell electron pairs of the central atom are considered both the pairs that form covalent bonds (called bonding pairs) and the pairs that are unshared (called nonbonding pairs or lo ne pairs). ? The nonbonding pairs help to insure the position of the atoms in the molecule or ion.Valence Shell-Electron-Pair Repulsion (VSEPR) theory allows the chemist to predict 3-dimensional shape of molecules from knowledge of their Lewis Dot Structure. In VESPR theory, the position of bound atoms (ligands0 and electron pairs are passd relative to a central atom. Once the ligands and lone pair electrons are positioned, the resulting geometrical shape presented by the atoms only (ignoring lone pairs) is used to describe the molecule. Electron Density and Molecular Geometry d(Be-Cl) = 0,117 nm? = 180 Linear (B-F) = 0,130 nm ? = one hundred twenty Triangular Planar d(S-O) = 0,150 nm ? = 109 . 5 Tetrahedral d(P-Cleq) = 0,202 nmd(P-Clax) = 0,214 nm? (ClPCl) = 90 ? (ClPCl) = 120 Triangular Biplanar d(Xe-F) = 0,190 nm? = 90 Octahedral 3. Apparatus and Materials 2- Modeling Clay (diff. colors) 1 Wire (3mm. diameter, 5ft. long) 1- Protractor 4. Procedure 4. 1. Determine t he molecular structure of the compounds listed in the table. 4. 2 contain the table provided for the experiment. 4. 3 Construct the molecular models for each compound. 4. 3. Use color for the central atom diff. from the attached atoms. Use one color for the attached atoms. 4. 3. 2 Make a 2-inch diameter central atom X and ? inch diameter for the attached atoms Y. 4. 3. 3 Cut the wire into 3 inches long. 4. 3. 4 subjoin the central atom X to the Y atoms based on the arrangement. 5. MolecularFormula BondAngles MolecularStructure No. ofBond Pairs No. ofLone Pairs AngularGeometry BeCl2 180 2 0 Linear BF3 120 3 0 TrigonalPlanar SO4 109. 5 4 0 Tetrahedral PCl5 120 5 0 TriangularBipyramidalXeF6 90 6 0 Octahedral 6. Questions 1. What is valence electron? Give its importance. In chemistry,valence electronsare theelectronsof anatomthat can participate in the formation ofchemica bondswith other atoms. Valence electrons are their own electrons, present in the free neutral atom, that comb ine with valence electrons of other atoms to form chemical bonds. In a singlecovalent bondboth atoms contribute one valence electron to form ashared pair. Formain group elements, only the outermost electrons are valence electrons.Intransition metals, some inner-shell electrons are also valence electrons. Valence electrons can determine the elements chemical properties and if it will bond with others or not. When two atoms approach each other and react with each other, it is their outer shells that come into contact first, and it is therefore the electrons in their outer shells that are normally involved in any chemical reaction. So it is the number of electrons in an atoms outer shell that determines, to a large extent, how that element will react chemically.