Orbital Representation Tutorial

Tutorial for Experiment: Orbital Representation

EXAMPLE: Construct an orbital representation of NH3.


  1. Write the Lewis electron dot formula for NH3.



  2. Determine the type of hybrid orbitals on the nitrogen atom in NH3. See Flow Diagram for help.




  3. Sketch relative energy level diagrams for the atoms in order to identify the orbitals that can be linearly combined to form bonding molecular orbitals.



  4. Select "sp3" (place cursor on sppp Orbitals to highlight it in dark blue and click the left mouse button) from the Components pop-up menu .



  5. Select "N" (highlighted in dark blue) from the Element pop-up menu as the central atom.



  6. Place the cursor at the point in the window where you wish to draw the isodensity surface, press the left mouse button and move the mouse slightly up or down.



  7. One of the sp3 hybrid orbitals on the nitrogen atom and the 1s atomic orbital on the hydrogen to the right of the nitrogen atom can linearly combine to form a bonding molecular orbital . A qualitative representation of the isodensity surface of this bonding molecular orbital can be constructed by overlapping the isodensity surfaces of the sp3 hybrid and 1s atomic orbitals. Since the isodensity surface of sp3 hybrid orbital on the right is in the plane of the page, we will select the "s" isodensity surface "In the Plane" of the page from Components pop-up menu.



  8. Next, select "H" (highlighted in dark blue) from the Element pop-up menu .



  9. Place the cursor to the right of the nitrogen atom, and click the left mouse button . If you wish to change the color of the "s" isodensity surface, continue to press the left mouse button and move the cursor horizontally until the color changes from blue to red.



  10. To move the representation of the isodensity surface of the 1s atomic orbital, place the cursor over the isodensity surface. When the chemical symbol for the hydrogen atom is "highlighted", press the right mouse button to display the pop-up menu. Select "Move" from the menu and click the left mouse button.



  11. Move the cursor to the left until the isodensity surface of the 1s atomic orbital overlaps the isodensity surface of the sp3 hybrid orbital on the right, and click the left mouse button.



  12. The representations of the isodensity surfaces of the remaining bonding molecular orbitals are constructed in a similar fashion (Steps 7 - 11). The isodensity surface of one of the sp3 hybrid orbitals on the nitrogen atom is above the plane on the page. The "In Front of the Plane" representation of the isodensity surface of the 1s orbital is chosen to overlap with this sp3 isodensity surface. The "Behind the Plane" representation of the 1s isodenstiy surface overlaps with the third sp3 isodensity surface.



  13. Select "Electron Pairs" (highlighted in dark blue) from the Components pop-up menu.



  14. Add four pairs of electrons to the right of the isodensity surfaces.



  15. Move one pair of electrons inside each representation of an isodensity surface of a bonding molecular orbital. These electron pairs identify the "occupied" molecular orbitals and correspond to the bonding pairs of electrons in the Lewis electron dot formula for NH3. The actual isodensity surfaces, of which these drawings are rough representations, enclose the regions in space in which there is at least 98% probability of finding the electron pair. The last pair of electrons is placed in the representation of the empty sp3 isodensity surface. This pair of electrons is the lone pair in the Lewis formula for NH3.



  16. To label the "sp3" isodensity surfaces, select "sp3" (highlighted in dark blue) from the Label pop-up menu on the tool bar.



  17. Add four "sp3" labels to the right of the representation.



  18. Move one label inside each sp3 isodensity surface.



  19. Select "s" (highlighted in dark blue) from the Label pop-up menu on the tool bar and "1" as the value of the quantum number n from the Quantum Number n pop-up menu.



  20. Place one "1s" label next to each isodensity surface of a 1s atomic orbital.



  21. Label the isodensity surface with the lone pair of electrons by selecting "Lone Pair" (highlighted in dark blue) from the Label pop-up menu.



  22. Place the "Lone Pair" label above the isodensity surface.



  23. Next, select "Arrow" (highlighted in dark blue) from the Label pop-up menu.



  24. Place the arrow to the right of the drawing, and then move it directly between the label and the isodensity surface with the lone pair.



  25. Finally, label the isodensity surfaces of the bonding molecular orbitals in a similar fashion.