Sadava9-2

__Level 1 – Answers to these questions are pretty clearly stated in your book__. 1. What are the most common elements in a human cell? 2. What are ions? Distinguish between cations and anions. 3. What is the difference (in terms of energy) between an electron in the orbital closest to the nucleus and one in an orbital further away? Why does this difference exist? 4. How do non-polar covalent bonds differ from polar covalent bonds? 5. What is the difference between a single covalent bond and a double covalent bond? 6. What is the strongest type of chemical bond? 7. How would you define “electronegativity” in your own words? 8. If hydrophobic interactions and van der Waals interactions are so weak, why do we have to care about them? 9. Distinguish between hydrophobic and hydrophilic molecules 10. What is a buffer? How do they work? Why are they necessary in biological systems? Give an example.

__Level 2 – Answers to these questions are not directly stated by the authors. You must “read between the lines” to answer them.__ 11. Helium has an atomic number of 2 and atomic mass of 4. Explain. 12. Sketch six molecules of water, indicate their polarity, and how H bonds will form between them. 13. Explain why a hydrogen atom will usually participate in only one covalent bond, while carbon usually participates in four. 14. Compare magnesium + chlorine (two elements with a big difference in electronegativity) with carbon + nitrogen (two elements with a somewhat smaller difference in electronegativity between them). Which pair is most likely to form an ionic bond? Why? What type of bond is the other pair most likely to form? 15. Explain the difference between a hydrogen bond and a covalent bond in which one of the atoms happens to be a hydrogen. __Level 3 – These questions ask you to go farther and read //beyond// the lines.__ 16. Why does an oxygen atom form a polar covalent bond when paired with a hydrogen atom, and a nonpolar covalent bond when paired with a nitrogen atom? 17. Why isn’t CO2 bent and polar like H2O? 18. Why is H2O much more likely to participate in chemical reactions than CO2? 19. Is liquid CO2 (yes, it does exist) likely to have a high heat of vaporization like water does? Why or why not? How about CO2’s cohesion capability compared to water’s? 20. Using the above picture and your answer to question 3, explain why the electrons in carbon dioxide and water have much less energy than those in methane and O2. (Hint: when would a negatively charged electron be “happiest”?)