PHYS 1090: Fundamentals of the Physical Universe

Unit 11: Electrons and Bonding
Originally due November 2, 2011, but now postponed until December 2
20 points

Yes, this is due at the same time as the Unit 10 homework.  That is because there are more units in the course than weeks in the semester.

Answer one, and only one, of the following questions.

These questions are for you to combine different ideas from the unit and apply them to situations not directly addressed in class or in the textbook.  Think about the situation, and about the physics that applies to it.  See me for help if you are stuck.

1. What we’re made of.

Why do atoms exist?  To answer this, you will need to answer two questions.

• Why don’t electrons just collapse into the nucleus?  After all, electrons are negatively-charged, and protons are positively-charged, so they attract each other strongly.  Shouldn’t they just stick together?
• Why do additional electrons (after the first two) reside in ever-farther orbitals instead of the one with the lowest energy?
2. Foundations of chemistry.
• Why do an atom’s valence electrons dictate its chemical reactivity?
• Why do elements in the same column of the periodic table have similar chemical properties?
• What does an element’s column in the periodic table signify?
3. Dot structures.

The dot structures that we created in class to understand covalent bonding are a model.  In other words, they are a representation of some aspect of reality, not the reality itself.

• What is it that dot structures represent?  What do they help us understand or visualize?
• What about molecules do dot structures not represent well?  Is there anything about a dot structure that may give someone a wrong idea about the molecule it repersents?
4. VSEPR theory.

Explain as well as you can what determines the shape of a molecule.  Give examples of at least two molecules and why they take the shape they do.  Explain it in terms that would make sense to a sixth-grader.

5. Prior learning.

This unit progressed from identifying the valence electron configurations of atoms through the bonds formed with other atoms to the shapes of the resulting molecules.

• What of this material had you been taught before?  When?
• Did you learn it differently then?  If so, how did you learn it before?
• Does anything you learned in this class not make sense in light of what you learned before?  If so, what is it?

If you never encountered any of this material before this class, answer a different question.

6. Tools.

In class this week, I provided several aids to help you learn the material: periodic tables helped you determine the valence electron configurations of atoms, paper squares and beans helped you keep track of atoms and valence electrons in molecules, and foam balls and toothpicks helped you visualize the spatial connectivity of atoms in molecules.

• If you used any of these tools, How did you use them?  Why did you decide to use them?  Did you eventually not need them any more?
• Can you thnk of any other tools that could be used to learn the content of this unit?  If so, what would they be, and how would they be used?
7. Your struggles.

Identify a part of this unit that was difficult for you, or a part in which you initially made a lot of mistakes.

• Why, do you think, did you have difficulty at first?
• What happened so that you can now do it?  Or, what still confuses you about it?

If no parts of this unit were at least initially difficult for you, answer a different question.

Take your choice of these tasks.  Do not submit answers to more than one of them.  Just choose one, and submit it.  Your answer should thoroughly address all points of the question.  An adequate answer will be several paragraphs long.

If you submit any part of this assignment as an electronic document, upload it (or them) to WyoSakai using the “Assignments” tool.  That way I will be able to find them easily and I will not tend to lose them.  Or, you may enter your text directly into the “Assignments” tool.  Hard copy submissions are also allowed.

Reminder: If you submit your answer in hard copy, do not turn in paper that has ragged edges!  If you write your work in a spiral-bound notebook, trim the edge before submitting it.  Papers with ragged edges will be returned unmarked.