Study Guide 2
Last revised: Thursday, August 31, 2000

Topic: Chemicals in the Cell I.

Chapter 2. Once you start looking inside a cell, everything is chemistry. This chapter and the accompanying lecture review basic chemical concepts from which to build an understanding of biochemistry, the "molecules of life". This will be review for most of you, so shake the cobwebs off your brain cells and make sure these terms and ideas are comfortable and familiar. When you are ready, try practice quiz 2 to make sure you've "got it".

1. Terms. Be able to recognize and correctly apply the following terms:

   Element	Trace element	Neutron	Proton
   Electron	Atomic number	Atomic weight	Isotope
   Electron shell	Valence electrons	Covalent bond	Double bond
   Double bond	Nopolar bond	Polar bond	Ionic bond
   Hydrogen bond	Van der Waals bond	Electronegativity

   
   
2. What does a dalton measure? What is the approximate weight of a proton? A neutron? An electron?
3. Explain why the chemical properties of an element are defined by the number of protons, using the concept of electron shells.
4. Would knowing that an atom had a certain # of electrons allow you to tell what kind of element it was? Why or why not? Would knowing the number of protons tell you what kind of element it was?
5. Which of the following are elements? Water, Sodium, Carbon dioxide, Sugar, Oxygen, Carbon.
6. How does the abundance of elements in the earth’s crust compare with the abundance of elements in living tissue?
7. What 6 elements are required in largest quantity by all life? What additional element is required in large quantity by vertebrate animals?
8. Animals with nervous systems require substantial concentrations of two elements that are used to create electrical charges across membranes. What are these two elements?
9. Most trace elements are (choose one): __ metals __ salts __ gases __ noble gases
10. What is an isotope? Are all isotopes radioactive? The substances ²H and ³H differ in that ³H has one more ____________ than ²H
11. Compared to normal ¹²C, how does the radioactive isotope ¹⁴C differ?
12. Note the discussion of electron orbitals and shells on p. 27. The correct description of electron geometry is based on orbitals. The concept of electron shells is an oversimplification that works only as a first approximation. However, for purposes of Biology 107, we will ignore the actual orbitals and use the concept of outer electron shells to predict valences and chemical bonding. Be aware that this is somewhat of a fiction, which your chemistry teachers will undoubtedly clear up in some detail.
13. What are the valences of each of the CHNOPS elements?
14.  What is a covalent bond? How does it differ from an ionic bond? A hydrogen bond? A Van der Waals bond?
15. Which of the following structural formulas has incorrect valences? (more than one may be incorrect)
    (a) NH₃ (b) H=C=H (c) SH₃ (d) O=C=O
    
16. How many errors can you find in the following structural formula? (Hint: look at each element to see if its valence is properly matched with the number of bonds shown)
    
    
    
    
17. The concept of "polarity" is very important, so be sure you understand this. Note that, in most chemical bonds between different elements, electrons are shared unevenly, resulting in polarity. What are some examples of chemical bonds that are nonpolar?
18. What is the difference between a polar and a nonpolar bond? Which of the following covalent bonds is not polar (note: not all bonds have been filled in)? More than one answer may apply.
    (a) — C—O— (b) —C—H (c) —C=O (d) —O—H (e) O=O
19. Why are ionic bonds weaker in aqueous solutions than in a crystal?
20. Why are weak chemical bonds important for living systems?
21. Is the shape of a molecule important in understanding its chemistry? Why or why not?

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