Bond Polarity Activity AP Chemistry 2 points Date: Hour: In this activity, you will learn about bond polarity using the online software WebMO.

Transcription

1 Bond Polarity Activity Name: AP Chemistry 2 points Date: Hour: In this activity, you will learn about bond polarity using the online software WebMO. Background Knowledge: 1) What types of chemical bonds are there? 2) If given a chemical bond (such as C H), how can you tell what type it is? 3) Which of these are considered ionic bonds? A) Sn Pb C) N O B) Ca F D) Br Br 4) Which of these are considered covalent bonds? A) O Ni C) O F B) Cl Na D) O O 5) Take 5 minutes to research electronegativity, polar covalent bonds, and dipole moment. (You may use the Internet, your notes, and/or a textbook.) Record what you find here: 6) Discuss your findings with your partner. (Feel free to add information that your partner found.) Be ready to share your findings with the class.

2 7) Use your findings to predict the ranking of the following bonds from most ionic to most covalent: H Br, H Cl, H F, H H, and H I, and H Na. 8) Discuss the reasoning behind your predicted ranking with your partner. 9) Write at least one complete sentence describing the reasoning behind your predicted ranking: 10) Launch WebMO. (Each person should launch WebMO on his/her own computer.) o To begin, go to the website o Click on the link Log in to the WebMO server (See teacher for username and password) o Choose New Job and Create New Job 11) Create a data table below. Columns should include bond, dipole moment, and ranking.

3 12) Build each bond listed in your predicted ranking separately in WebMO. Remember to choose clean-up (comprehensive idealized), then choose Mopac as your engine, Geometry Optimization as your calculation, and to add your initials to your job name. From your job results, scroll down and record the dipole moment of the chemical in your data table. Click the magnifying glass next to dipole moment and draw any arrows you see in your data table. 13) Discuss any patterns you see in your data table with your partner. 14) Write at least three sentences about any pattern(s) you found: 15) Based on your data table, what does the arrow represent? 16) Based on your data table, how can you predict the direction of the arrow (or if there is an arrow at all)? 17) Based on your data from WebMO, rank the bonds from most ionic (#1) to most covalent (#6). Put your rankings in your data table. 18) Does an ionic bond have a larger or smaller dipole moment than a covalent bond? Include evidence from today s activity with your answer. 19) Why do you suppose there is a difference between the dipole moments of ionic bonds and covalent bonds? 20) Was your final ranking the same or different than your predicted ranking?

4 21) Now using the knowledge you gained from this lesson, we will build five molecules and look at polarity (and dipole moment). Create a data table below. Columns should include molecule name, structure, and dipole moment. 22) The five molecules will be methane and methane substituted with a halogen. The second molecule will have one halogen atom, the third will have two of the same halogen atom, and so on. Write the names and structures of the five molecules in your data table above. 23) Now use WebMO to build your molecules. Remember to choose clean-up (comprehensive idealized), then choose Mopac as your engine, Geometry Optimization as your calculation, and to add your initials to your job name. Record the dipole moments and draw any arrows you see. 24) Based on the WebMO data, what pattern(s) do you see? 25) Were there any molecules that surprised you? If so, how did they surprise you? 26) Use WebMO to make a very ionic bond (the most ionic you can possibly make). Record your findings and evidence here:

5 27) Finally, build the molecules water (H 2 O), ammonia (NH 3 ), carbon dioxide (O=C=O), cis- 1,2-dicholoethene, and trans-1,2-dichloroethene. Draw their structures, record their dipole moments (if any), and draw in the dipole moment arrows (if any). Now WITHOUT using WebMO, answer the following questions: 28) Which of these would have the largest dipole moment? A) Si Se C) Cu Fe B) Br F D) Cl Rb 29) In the bond Cl C, in which direction would the dipole moment arrow point? C) At the Cl C) At both the Cl and the C D) At the C D) There would be no arrow 30) Draw the structure for propane. Predict whether there would be a dipole moment arrow. If you predict there will be, draw in your prediction. 31) Draw the structure for 2-fluoropropane. Predict whethere there would be a dipole moment arrow. If you predict there will be, draw in your prediction. 32) What is one question you still have related to information from today s activity?