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Deducing Lewis DiagramsUsing molecular formulas to determine Lewis diagramsThere are many molecular compounds for which it is not easy to predict the formula based on the principles we've just been using. Even so, you will sometimes need to draw Lewis diagrams for them. One reason for doing this is to determine molecular shapes and properties. In such cases you will be given the name or molecular formula and be asked to draw the Lewis diagram for it. Sometimes that will be an easy task and the dots will just fall into place. Other times it will not be so easy. Let me give you some guidelines that I use in such cases. Your textbook and other instructors use different approaches. So, if my method doesn't work for you, try one or more of the others.
This approach is somewhat intuitive - presumably, you think like an atom and put your electron dots where they will best accommodate the atoms to which you will be bonding. Other ApproachesOther, more systematic approaches can also be used. If you have trouble using the previous approach try using the "Systematic Approach" shown in example 18 in your workbook. Your textbook also outlines a method in the section on "Writing Lewis Structures." Or you can get some additional help from an instructor or other students to work out an approach that works best for you. Examples and PracticeUsing the other pages in this section you can work through a couple of examples using the method I have described. The formulas let you practice using the guidelines, or try using the other options. (These examples are also shown in examples 16,a-b in your workbook, and the practice is in exercises 16,c-e and 17.)
E-mail instructor: Eden Francis Clackamas Community College |
