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VSEPR model and molecular shapes

Science and Technology

This exercise heps you to understand VSEPR model and orbital hybridization concept to predict molecular shapes.

Part A:  Using the VSEPR model to predict the structures for BeH2, H2O, BH3, NH3, and CH4 and the angles of the central atoms.

Part B:  Use Basic QChem Edu or Basic QChem tools in Avisto to find the stable structures for the above molecules.  You can download these tools from Astonis.


  1. Use MolDesign to create BeH2, H2O, BH3, NH3 and CH4 then send them to your workbench.
  2. Use Basic QChem Edu or Basic QChem tool to search for stable structures of these molecules.
  3. Use PsiViewer to analyze the results (just double-click on the data sent out in Step 2). 
  • Measure the angle of the central atom by click on the atoms defining the angle.
  • In the MO tab, select to plot the delocalized orbitals.  Classify these orbitals as bonding, anti-bonding, or non-bonding.
  • In the MO tab, select to plot the localized orbitals.  For each molecule, plot all localized orbitals and notice the size of the electron lone pairs on H2O and NH3.
  • On the MO coefficients panel, select not to plot contributions from the Hydrogen atoms, then replot to view the hybrid orbitals of the central atom.
  • 4. Rank the size of the angle in H2O, NH3, and CH4. Do your results confirm the prediction regarding the relative values of these angles predicted by the VSEPR model?
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