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Molecule geometry and shapes

 

Lab: Phet Molecular Shapes VSEPR Activity                                                                        

Log on to https://phet.colorado.edu/en/simulation/molecule-shapes either by Googling “phet simulations molecule shape.”   Click on the play button in the center.

Introduction click here for help

Atoms bond to satisfy their need for more electrons.  If both atoms have high electronegativities (are nonmetals), atoms will share electrons to satisfy the Octet Rule – every atom wants 8 electrons to fill the s and p orbitals in the outer energy level.  But, as you will see, if the electronegativities are high enough and both atoms unwilling to give up electrons, sometimes atoms can deviate from and not follow the Octet Rule.

Because electrons have a negative charge and atoms occupy space, bonds and electrons will spread out as much as possible.  Since we write in a two dimensional plane on paper, it is difficult to visualize the true geometry of these molecules.  This activity and the program you are about to use allows us to visualize on a more 3-dimensional scale.

Part 1 – Generic Molecules

Fill in the chart below by creating the generic molecules below.  On your screen in the lower left corner, click on “molecule geometry.”  Add atoms and electron pairs as needed to produce the generic formula.  Once the molecule is assembled, click and drag the screen to spin the atom around.  Click on the “Show bond angles.”  Use the following key:

click here for help

• A – central purple atom – cannot be removed
• B – single bonded white atom
• C – double bonded white atom
• D – triple bonded white atom
• E – Electron pairs not bonded (lone pair)

 

In each box:

1. Take a screenshot from your computer and place it into the box
2. Identify which molecule from the HW yesterday corresponds to the box
3. Write the Molecular Geometry (MG)
4. Look at the central atom, is its octet satisfied?

 

 

Molecule		Molecule
AC2                     Molecule from HW: MG ___________________________   Octet?  ______		ABE3                   Molecule from HW: MG _____________________________  Octet?  ______

 

 

AB3E                   Molecule from HW: MG _____________________________  Octet?  ______		AB                   Molecule from HW: MG _____________________________  Octet?  ______
ACE2                   Molecule from HW: MG _____________________________  Octet?  ______		AB2E2                   Molecule from HW: MG _____________________________  Octet?  ______
AB2C                   Molecule from HW: MG _____________________________  Octet?  ______		ABD                   Molecule from HW: MG _____________________________  Octet?  ______
AB4                   Molecule from HW: MG _____________________________ Octet?  _____		ADE                   Molecule from HW: MG _____________________________  Octet?  ______

 

 

 

Part 2 – Octet Rule Breakers

While still in the “Real Molecules” tab, select the following molecules.  Take a screenshot from your computer and place it into the box, write the molecular geometry, and write how many electrons are on the central atom.

Molecule		Molecule
SO2                                                                                  MG _____________________________ Electrons?____		XeF2               MG _____________________________  Electrons?____
ClF3                 MG _____________________________  Electrons?____		SF4                 MG _____________________________  Electrons?____
XeF4                                                                                MG _____________________________  Electrons?____		BrF5               MG _____________________________  Electrons?____
PCl5                 MG _____________________________  Electrons?____		SF6                 MG _____________________________  Electrons?____

 

 

Molecule geometry and shapes

 

 

Post Lab Questions

1. The program did not give a bond angle to a molecule consisting of only two atoms.  Why?  Think geometry class.

 

 

1. What happens to the bond angle within a molecule as you add more bonds to the central atom?

 

1. How does a lone pair affect the molecular geometry of a molecule?

 

 

1. Explain how the “octet rule breakers” violate the octet rule? Did all of these “octet rule breakers” violate the octet rule the same way?

 

1. Did the molecular geometry of the “octet rule breakers” match any that did follow the octet rule? If so which ones and why?