PhET Activity for MS-PS1-1: Molecule Shapes

DIRECTIONS:
1. Click on the 'Model' image button to enter the model-building section.
2. Observe the molecule in the center. This is the default setup with a central atom and two single bonds, forming a linear shape.
3. In the 'Name' panel on the bottom left, check the box for 'Electron Geometry'.
4. Now, check the box for 'Molecule Geometry'.
5. In the 'Options' panel on the right, check the box for 'Show Bond Angles'.
Take 2-3 minutes to freely explore. Try rotating the molecule by clicking and dragging it. What do you observe about the initial shape, geometries, and bond angle?

QUESTION: Are you acquainted with the tools in this simulation?

DIRECTIONS:
1. Ensure you are in the 'Model' tab with a central atom and two single bonds from the previous step.
2. In the 'Lone Pair' control panel on the right, click the 'Lone Pair' button once.

QUESTION: Adding one lone pair to a central atom that has two single bonds changes the Electron Geometry to ___ and the Molecule Geometry to ___.

(a)  

DIRECTIONS:
1. Starting with the 'Bent' molecule from the previous slide (2 bonds, 1 lone pair), click the 'Lone Pair' button again.

QUESTION: You now have a molecule with 2 bonds and 2 lone pairs. What is its Molecule Geometry and ideal bond angle according to the model?

DIRECTIONS:
1. Starting with the molecule from the previous slide (2 bonds, 2 lone pairs), click the 'Add Lone Pair' button one more time.

QUESTION: With 2 bonds and 3 lone pairs, the five electron domains arrange in a Trigonal Bipyramidal electron geometry, but the resulting Molecule Geometry is (a)   .

DIRECTIONS:
1. Starting with the linear molecule from the previous slide (2 bonds, 3 lone pairs), click the 'x' button next to one of the lone pairs in the right panel to remove it.
2. Now, in the 'Bonding' panel, click the 'Add Single Bond' button once.

QUESTION: The molecule geometry is 'T-shaped'. Based on VSEPR theory, explain why the lone pairs occupy the equatorial positions rather than the axial positions in a trigonal bipyramidal electron geometry.

DIRECTIONS:
1. Click the red 'x' in the lone pair box to remove 1 of the lone pairs.

2. 2. Click the 'Single Bond' button once to create the T-shaped molecule (3 bonds, 2 lone pairs).

3. 3. Click the 'Single Bond' button again to add a fourth single bond to the molecule.
   
   QUESTION: What are the Electron Geometry and Molecule Geometry for a molecule with 4 single bonds and 2 lone pairs?

DIRECTIONS:
1. Click the 'Remove All' button in the right panel to clear the screen.
2. Click the 'Single Bond' button three times.
3. Make sure the 'Molecule Geometry' and 'Show Bond Angles' boxes are checked.

QUESTION: A molecule with three bonding groups and zero lone pairs has a ___ geometry with bond angles of ___ degrees.

(a)  

DIRECTIONS:
1. Click the 'Real Molecules' tab at the bottom of the screen. The simulation will default to the water molecule (H2O).
2. Check the boxes for 'Electron Geometry', 'Molecule Geometry', and 'Show Bond Angles'.

QUESTION: What is the Electron Geometry of the water molecule (H2O)?

DIRECTIONS:
1. With the water molecule (H2O) displayed, observe the 'Real' bond angle shown on the screen.
2. Now, click the 'Model' toggle switch at the top center of the screen to see the idealized geometry.
3. Observe the 'Model' bond angle and compare it to the 'Real' one.

QUESTION: The ideal ('Model') bond angle for a tetrahedral electron geometry is 109.5°, but the 'Real' bond angle in water is 104.5°. Why is the real bond angle smaller?

DIRECTIONS:
1. Ensure you are in the 'Real Molecules' tab.
2. Select 'BF3' from the molecule dropdown menu on the right.
3. Ensure all geometry and angle boxes are checked.

QUESTION: The BF3 molecule has three bonding pairs and no lone pairs, giving it a (a)   shape.