Molecular Polarity Modeling Lab Question: What molecular shapes and bonding types lead to molecular polarity? Procedure/Data Collection – Italicized and underlined sections below should be recorded in the notebook as data!

1. Open the PhET – “Molecular Polarity” simulation on your computer. The “two atom” tab should open and show you a molecule with the generic atoms “A” and “B” attached.

2. Note the difference in electronegativity values on the slider located for each of these two atoms. Activate all check boxes in the “View” section (Bond Dipole; Partial Charges; Bond Character). Move the slider for atom “A” and write a quick summary of the changes occurring for the three checked values.

3. Now check the box for Electrostatic Potential in the “Surface” section; repeat the slider with atom “A” and record the effect.

4. Move the slider for atom “B” to more and atom “A” to less. Check the Electron Density box in the Surface section. Observe the effect…then check the Electric Field box and record your observation. Play with the sliders for both atoms and drag the molecule around and record the response.

5. Examine the Table of Electronegativity Values from our Molecule Shape lab and the LDD for the diatomic molecules from the following list. Assume the atom EN slider is marked in 0.5 Electronegativity values and set these values for the following molecules. Record the speed and direction of the molecule response as you drag the molecule to vertical and allow it to change.

HI; Cl2; HF; CN1- Draw the LDD for these molecules (as close to 3-D as you are comfortable) and then write in the bond dipole arrow, partial charge notations (δ+ or δ-) and indicate approximate bond character.

6. Draw the LDD for the following three atom molecules and then click the “three atom” tab. Drag atoms A and C around the central atom B until the shape matches your diagram (consider VSEPR and our work in the earlier lab). Use your electronegativity table to approximate the electronegativity values on the slider for atoms A, B & C for the following molecules: [the central atom will always be atom B and sometimes your approximate angle will need to reflect the presence of a nonbonding pair on the central atom]

BeCl2; HBeCl (Be is the central atom); NO21- Now, write in the bond dipole arrow, molecular dipole arrow and partial charge notations (if present) on your LDD drawings.

7. Go to the Real Molecules tab and in the View box, check all except the Partial Charges box. Now, examine the first five molecules in the drop down menu and note the difference in arrows when you get to HF. Note how alike this is to your work in #5 above with the exception of the molecular dipole arrow! Draw a quick diagram of each of these.

8. Continue your analysis of the rest of the molecules and draw a quick diagram of each showing the molecular “dipole moment” or arrow.

9. For all of the molecules you sketched in #7-8, circle each molecule which contained a molecular dipole…these are the polar molecules.

10. If you are interested (and because I like even numbers) feel free to examine the electrostatic potential and electron density boxes and examine the molecules.

Data Analysis/Conclusion Important Statement: Anytime you are able to generate a molecular dipole arrow the molecule is

polar. If the molecular dipole arrow is not present then the molecule is nonpolar. 1. Why would it be incorrect to state all linear diatomic molecules are nonpolar? Why would it

be correct to state all diatomic elements are nonpolar? 2. Draw the HBr L.D.D. and write the expected Bond Dipole, Partial Charge, and Bond Character

symbols on this molecular diagram. Would you expect the HBr or the HI molecule to respond faster if an electric field was turned on? Explain.

3. Generate a clear statement in your own words which explains why one linear molecule (like BeCl2) is a nonpolar molecule whereas HBeCl, also a linear molecule, is polar. Make certain you address both the molecular geometry and the type and arrangement of bonded atoms. Additionally, explain why another three atom molecule (like NO2-) has identical atoms bonded to the central atom (same exact polar covalent bonds) and is polar.

4. Examine the tetrahedral diagrams you drew back in procedure #8 above for CH4 and CH3F. Explain why methane is drawn without a molecular dipole arrow yet fluoromethane does have one?

5. Draw the L.D.D. for ICl5 and PBr5 (these are both in the prior lab). Examine/imagine the 3-D shape of each of these molecules and then draw your expectations for the Bond Dipole arrows on each bond and any resulting Molecular Dipole Arrow. (If you are able to sketch these in 3-D…it could certainly help your understanding/explanation). Explain your results.

6. For each of the following pairs of molecules: (I) draw the L.D.D. and state the shape and bond angle(s) (II) draw the molecular dipole arrow (if present) on the L.D.D. (III) determine which of the pair is most polar and explain your reason for making this choice

(recall from the program…a larger molecular dipole arrow = more polar molecule)

a) carbon disulfide OR sulfur difluoride

b) nitrogen trichloride OR oxygen dichloride

c) boron trihydride OR ammonia (NH3)

d) chlorine OR phosphorus trichloride

e) silicon dioxide OR carbon dioxide

f) methane (CH4) OR CH2Cl2

g) silicon tetrabromide OR HCN

h) nitrogen trifluoride OR phosphorus trifluoride

7. Consult “Table I – Molecular Analysis” in the molecular shapes lab. Are you able to pick out

any shape names which will always lead to a molecule containing a molecular dipole arrow? Explain your answer.

8. The easiest way to apply the importance of determining whether a molecule is polar or nonpolar is based on the ability of substances to dissolve or mix with each other (and not separate out). The statement: LIKE DISSOLVES LIKE is very useful and relates the fact that nonpolar molecules will dissolve or mix with other nonpolar molecules (and vice versa for polar molecules). Good example: Oil and water do not mix (or cannot stay mixed) no matter how hard you mix them together. Which of the following substances should be able to mix with water? NCl3, Cl2, SiBr4, CS2, HCN