How are ionic bonds and covalent bonds different?

BIO181: Chemistry of Life

1. Define polar and nonpolar bonds using complete sentences. In your definition, make it clear what criteria you use to determine if a bond is polar or nonpolar.

2. How are ionic bonds and covalent bonds different?

3. What does electronegativity mean?

4. How do electronegativity values help us determine the type of bond created?

5. For each of the following molecules in the table below, determine if it is polar, nonpolar, or ionic. Show your work by listing the electronegativities of each element in the bond.

6. For each of the four molecules below, complete the following: a. Draw in the pair of electrons shared between atoms. Draw the electrons closestto more electronegative atoms or in the middle of the bond if the atoms are equally electronegative.

b. For each ATOM, determine if it has any electrons that are shared unequally, if so, write a partial charge (𝛿+ or 𝛿-) next to that atom.

c. Label all POLAR bonds. d. Label each of the molecules below as polar or nonpolar.

7. Label the following molecules as polar or nonpolar.

8. For each of the molecules below, draw the compound using a Lewis structure and then indicate whether that molecule is polar or nonpolar.

CH4 NH3 OH-

9. Answer the following questions using the diagram below:

a. Which molecule(s) are polar? What led you to this conclusion?

b. Which molecule(s) are nonpolar? What led you to this conclusion

c. Which molecule is “water-fearing” or “hydrophobic”? What led you to this conclusion?

d. Which molecule is “water-loving” or “hydrophilic”? What led you to this conclusion?

10. What is the relationship between polarity and hydrophobicity, in general?

11. For each of the following biological molecules, indicate whether the molecule is primarily hydrophobic or hydrophilic. For each molecule, justify why you indicated it was hydrophilic or hydrophobic.

a. 

b. 

c. .

d. 

12. Answer the following questions using the diagram below:

a. Draw in the shared electrons for the bonds that are shown in bold (like for the

unbolded bond above with the arrow pointing at it). b. Draw the partial charges on the atoms involved in the bonds that are bolded. c. Why is an attraction possible between the H and O involved in the hydrogen

bond (indicated with the dotted line) shown above?

d. Draw an alternative hydrogen bond between different atoms of these two molecules in the space below:

e. Go back to Question 9 model and draw in some of the possible hydrogen bonds in both mixtures.

13. For the following pairs of molecules, draw their structures and at least one hydrogen bond connecting them. If no hydrogen bond is possible between these two molecules, indicate that.

a. Water and CH3NH2

b. Methanol (CH3OH) and Carbon dioxide

c. Methanol and CH3NH2

14. Hydrogen bonds can occur between molecules (intermolecularly), or within different parts of a single molecule (intramolecularly). Hydrogen bonds are a crucial component of biomolecular structures. In the following drawings, draw in any hydrogen bonds that are possible between atoms within the same molecule or between different molecules:

15. Biomolecules like DNA, proteins, and carbohydrates depend on hydrogen bonds to maintain their overall structure. However, each individual hydrogen bond is very weak. Using cellulose from question 14 as an example, explain how to resolve the apparent contradiction between these two statements.

To help you answer this question, we have provided two images. The first image illustrates hydrogen bonds within cellulose, and the second image illustrates how Velcro “sticks” together to make strong connections. Think about how Velcro works as you answer this question.

Cellulose Velcro

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