Enduring Understanding Paper Post-course Evidence Essay

Transcription

1 Amy Dewees MISEP Chemistry 512 Jacobs August 16, 2007 Enduring Understanding Paper Post-course Evidence Essay The Enduring Understanding that I have chosen to reflect upon is EU #2, which states: Learning and communication about chemistry is highly dependent on understanding the symbolism and epresentations of the discipline. Molecules can be represented in many ways and each representation has its own strengths and weaknesses. Therefore, the appropriate representation to use in a given context depends on what you are rying to get across about the molecule in question. This enduring understanding discusses representations of molecules and in this course many different epresentations of molecules were used, but this is not limited to the field of chemistry, other branches of science use epresentations to illustrate different things. In many areas of science graphs are used to display data and can be used to show trends or relationships. Pedigrees and punnett squares are representations used in biology to show the inheritance of raits in families. In evolutionary biology, cladigrams are used to show evolutionary relationships. Scaled models of the solar systems can be used in studying astronomy to show how the planets compare to one another. All of these epresentations have specific situations in which they are best applied and all have weaknesses. Some of the representations of molecules that were used were during this course were condensed formulas, structural formulas, Lewis structures, three-dimensional structures, and skeletal structures. A condensed formula, such as C 3 H 7 NO 2, allows one to easily calculate the molar mass or formula weight for the compound, but it does not provide nformation about the arrangement of the atoms within the molecule. A structural formula such as CH 3 COOCH 2 NH 2, provides enough information to draw a diagram of what this molecule looks like, such as a skeletal diagram. This makes t possible to determine the polarity of a molecule and the structural formula makes it possible to draw an accurate Lewis structure which can be used to find the bond angles within the molecule. Knowing the arrangement of the parts of the molecules can allow one to predict how it will react with other molecules and what types of intermolecular bonds it will be able to form, which will cause it to have particular properties. When studying proteins other representations were used including space filling, wire frame, ball and stick, backbone only, backbone and dots, and those showing polarity of the side chains. These different representations made it

2 makes it easier to see that enzymes are proteins and that the enzyme functions because the active site is complimentary to he substrate. Different representations may be useful for some students to understand complex topics such as DNA. I have students build models of DNA molecules to help them understand the structure and to better visualize the processes of eplication, transcription and translation. This is helpful in illustrating the basics of DNA and its related processes, but it acks some of the detail that can be provided by more detailed illustrations found on the internet and in textbooks. The manipulatives do not accurately show the bonding within the DNA molecules and the shapes of the various nucleotides and it adds to the misconception that hydrogen bonds are inside a molecule because the bonds that are used to represent he hydrogen bonds between the nitrogen bases are the same as those that represent the covalent bonds within the DNA molecule. Pedigrees are representations used in genetics to illustrate inheritance of traits within a group of related ndividuals. These diagrams can then be used to determine the type of inheritance that is responsible for the trait of nterest. Reflective Statement Prior to this class, I was aware of the various methods of illustrating or representing molecules, but I never really hought about which type of representations should be used in specific situations or why. The type of representation I used in different situations were usually dictated by a professor or textbook and again, I never really considered if it was he best one or why another representation would be better. This is an area that my students often struggle with and I never felt confident in why their textbook used different representations and I often found myself wishing I could present hings differently. At the conclusion of this class, I feel more confident in understanding the strengths and weaknesses of he different molecular representations we used in class. I have included a quiz question (Attachment 1) that involves drawing skeletal structures from a condensed ormula. In this question, two diagrams were drawn from one condensed formula, illustrating that condensed formulas

3 happens to the kinetic energy of molecules when they are heated and why increasing temperature speeds up a chemical eaction. Both of these pieces of evidence also illustrate the use of accurate scientific language because new terminology specific to this course was used in each example. This is especially true of the second piece of evidence. This enduring understanding also illustrates that there are some topics that can be applied to more than one area of science. As stated before, different representations can be used to illustrate relationships, processes or reactions and some are better than others. Deciding on which type of representation is best for a particular situation is dependent on what it will be used for.

4 Evidence 1: Chemistry Jacobs Quiz #2: Organic groups and reactions 1. Draw two line (skeletal) structures for compounds with the condensed formula C 3 H 6 O 2. These two isomers must contain two different functional groups. Circle the compound that is expected to be more soluble in water, and explain your choice.

5 Evidence 2: