VSEPR and Molecular Modeling Lab

VSEPR and Molecular Modeling Lab For this lab, there will be no formal lab report. You will follow the instructions below and complete the chart. You must turn this document in with all parts filled in according to the instructions. Objectives 1. To predict structure and polarity of a compound based on its Lewis Dot and VSEPR Theory Background Many molecules obey the octet rule and their Lewis-Dot structures are straightforward. Recall that to draw the Lewis-Dot structure of a molecule obeying the octet rule, eight electrons on each atom (except hydrogen and a few others) are arranged in four pairs. Each pair either participates in a covalent bond or is present as a lone pair. Some molecules have an odd number of valence electrons or may have an expanded octet. According to the Valence Shell Electron Pair Repulsion (VSEPR) Theory, the areas of high electron density move as far apart from each other as possible, without leaving the atom. It is the repulsion of lone pairs of electrons that causes the geometry or molecular structure of the molecule. The molecular shape is determined by the positions of the atoms in a molecule, which are influenced by bonds and lone pairs. The possible shapes for the molecules in this lab are linear, bent, trigonal pyramidal, tetrahedral, and trigonal planar. Shape Linear Trigonal planar Tetrahedral Trigonal bipyramidal Octahedral Bent (V shaped) Trigonal pyramidal Bent (V shaped) SeeSaw T Shaped Linear Square pyramidal Square planar Electron Domains 2 3 4 5 6 3 4 4 5 5 5 6 6 Number of Lone Pairs 0 0 0 0 0 1 1 2 1 2 3 1 2 Bond Angle 180° 120° 109.5° 90° (ax) and 120° (eq) 90° 95° <109.5° 104.5° <90° (ax) and <120° (eq) <90° (ax) 180° <90° 90° Hybridization sp sp2 sp3 sp3d sp3d2 sp2 sp3 sp3 sp3d sp3d sp3d sp3d2 sp3d2 VSEPR and Molecular Modeling Lab Knowing the geometry of a molecule allows one to predict whether it is polar or nonpolar. Polarity of a molecule is also affected by the difference in electronegativity between the values of the individual atoms in a bond. A bond that is polar has a positive and a negative end. A bond between two identical atoms or two atoms with similar electronegativities is nonpolar. The symmetry of a molecule with polar bonds determines the molecular polarity. To investigate the shapes of the molecules in this activity you should use the following molecular simulator to build the bond pattern. The molecular formulas, the Lewis-Dot structures, sketches of the molecules, the names of the molecular shapes, the approximate bond angles, and polarities will be recorded in a data table. Electronegativity VSEPR and Molecular Modeling Lab PROCEDURE 1. Print this worksheet, write on it, then scan to submit. See canvas for instructions on how to scan using your phone for free. If you do not have a smart phone you may take a picture and upload that. 2. If you do not have a printer working, you can just replicate the table on paper to fill out 3. Follow the column directions below 4. Do not forget to add snapshots of your Phet simulated molecules either to this table directly (if possible), or in a separate document labeled clearly. Either will be accepted. 5. Determine the molecular geometry of the molecules below, draw the Lewis-Dot structure, build this structure in the simulator, draw it by hand in 3-D using the wedge/dash convention and determine the polarity. Column 1 Determine the total number of valence electrons in the compound, molecule or ion, and write the number in the space Column 2 Draw the Lewis electron dot structure. Show ALL valence electrons (including lone pairs). Show formal charges on all atoms that have non-zero formal charge. Circle formal charges to distinguish them from the true ion charges. Column 3 Using VSEPR, identify the molecular geometry of the molecule around each central atom. If there is no central atom, write “no central atom” (for example, NaCl) Column 4 Build the model using the simulator at https://phet.colorado.edu/en/simulation/molecule-shapes Use the “model” mode; do not use the “real molecule” option since it will not have all of the molecules pictured. Take a snapshot using your computer by right clicking on your image and selecting “Take snapshot.” Then paste the image into the below worksheet where appropriate (or attach a separate page with all snapshots labeled). Column 5 Draw the molecule using wedged and dashed bonds to indicate the 3-D structure. Label all bond angles and any polar bonds. Column 6 Calculate the change in electronegativity for the bonds in the molecule. Indicate bond polarity. Column 7 Using the geometry and the ΔEN, identify whether the compound is polar or nonpolar. Go back to your sketch in column 5 and add an arrow to indicate the molecular dipole. . VSEPR and Molecular Modeling Lab 1 2 Species & Number of e- Lewis Electron Dot Structure 3 VSEPR Electron Geometry; Molecular Geometry 4 Model Screen Shot of Molecular Geometry (or add to blank document separately) 5 6 Sketch hand drawn w/ labeled Bond Angles and polar bonds (use dashes and wedges where appropriate) ΔEN, bond polarity 7 Molecular Polarity 1 CH4 109.5° 8 e - Tetrahedral; Tetrahedral C-H = 0.4, slightly polar Nonpolar 2 NH3 8 e - Tetrahedral; Trigonal pyramidal H 2O Tetrahedral 8 e N-H=0.84, O-H=1.24, Polar Polar - HCl 8 e- Linear H-Cl=0.95, Polar VSEPR and Molecular Modeling Lab N2 5 e- Linear N-N=0, Nonpolar Nonpolar Tetrahedral C-H= 0.4 C-Cl=0.61 Polar Polar Bent S-H=0.38, slightly polar Polar CH2Cl2 20 e- H 2S 8 e- HF 4 e - Linear H-F=1.78, Polar Polar VSEPR and Molecular Modeling Lab SO2 _6_ e- Bent S-O=0.86, polar Polar CO2 _16_ e- Linear C-O=0.89, Nonpolar CO _10_ e- Linear C-O=0.89 Polar Trigonal bipyramidal P-F=1.79 Nonpolar PF5 _40_ e- VSEPR and Molecular Modeling Lab C2H 2 10 e- Linear This model cannot be built in PHET C-H=0.4 Nonpolar Bent This model cannot be built in PHET O-H=1.24 Polar Trigonal planar C-O=0.4 Polar Trigonal planar S-O=0.86 Nonpolar Trigonal planar N-O=0.86 Nonpolar H 2O 2 14_ e- CH2O 12 e- SO3 32 e- NO324 e-