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Mary-Kate Perrone
Chemistry 512
August 16, 2007
Final EU Paper and Reflection
Enduring Understanding #2:
Learning and communicating about chemistry is highly dependent on
understanding the symbolism and representations of the discipline. Molecules can be
represented in many ways, and each representation has its own strengths and weaknesses.
Post-Course Evidence Essay:
In order to gain a deeper understanding of the underlying principles of Chemistry,
one should become familiar with the various types of symbolism and representations used
within the branch of learning. The representations of molecules entail many structural
figures and formulas. These structures and formulas of molecules allow scientists to
communicate within and outside the science community. According to W.M. Goodwin
(2007), Department of Philosophy at Swarthmore College, chemists have developed a
theoretical understanding of the phenomena they study. Yet, unlike other sciences, he
states that this understanding is not conveyed using mathematical equations and/ or laws;
rather, chemists employ diagrams to explain chemical principles. In particular, chemistry
utilizes structural formulas and potential energy diagrams to “carry the weight of the
discipline.” There are four types of formulas typically used in organic chemistry which
all provide different sources of information. They are molecular formulas, structural
formulas, condensed formulas and the line formula. This essay will further describe
examples of structural formulas and another representation of chemical principles known
as the potential energy diagram. As well, it will discuss the strengths and weaknesses
behind using these chemical symbols in the areas of Chemistry and in everyday
applications.
Some of the ways that molecular information can be depicted is through the
implementation of structural formulas. A structural formula can be defined as any
chemical formula that depicts the numbers and kinds of atoms in a molecule and the
bonds in which they are arranged (“Structural Formula,” n.d.). Typically the atoms are
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listed in order according to connectivity of their bonds. An example of this can be seen
in the representation for Ethane, which is a colorless and odorless gas used for fuel and
refrigerants.
H
—
H
H
|
|
C
—
C
|
|
H
H
—
H
ethane
An advantage to using this type of representation is that it shows the complete
structure of the molecule. In addition, structural formulas allow chemists to design
systems of synthesizing and enable them to predict compounds and their properties. In
other words, structure influences properties and determines shape. These symbols make
possible the visualization of the accurate structure and arrangement of the tiniest atoms of
a molecule (“Structural Formulas,” 2005-2006). On the other hand though, there are
disadvantages to using this means of representation. For instance, drawing out the
structural formula for larger molecules can get time consuming and require a lot of space
(Denniston, Topping, Caret, 2007). Therefore, to reduce time and space, structural
condensed formulas were developed. Here, the atoms in a molecule are placed in
sequential order to indicate which atoms are bonded to which. The structural condensed
formula for Ethane reads CH3CH3 (Denniston, Topping, Caret, 2007).
Learning structural/ condensed formulas paved the way for more representative
learning in Chemistry class. To ensure comprehension of these formulas, we practiced
drawing out the structures long hand in groups during POGIL Lab and on our own at
home. By understanding this type of symbolism, it allowed us to climb up the chemistry
ladder to learn other scientific principles. For example, structural and condensed
formulas were the ground work for understanding Lewis structures, which led to an
awareness of valence electrons and formal charges. These components aided in
determining resonance and isomers for molecules. Homework #1a required us to apply
all of the above components. We drew structural diagrams and identified any resonance,
formal charges, and isomers. As the course went on, these fundamental principles
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allowed us to scaffold our understanding so that we could eventually conceptualize bonds
between atoms and determine how those play a role in the formation of other
representative concepts such as primary, secondary, and tertiary structures of molecules.
As with all new information, it is purposeful to relate it to daily applications in
life. An example of usage of structural and condensed formulas can be found when an
individual receives a medicine prescription. Typically on the drug inserts, the structural
and condensed formulas are listed along with a line formula diagram of the molecule.
This is used to convey elemental information to pharmacists and other health
professionals. They then are able to use this information to make informed medical
decisions about other possible drug interactions (reactions) and treatments for ailing
patients.
As mentioned previously, potential energy diagrams are also used to describe
chemical principles. One of the most important fundamental scientific principles is the
notion of energy. Energy is defined as the ability to do work and can be classified into
either kinetic energy, defined as energy in motion, or potential energy, known as stored
energy (Denniston, Topping, Caret, 2007). Potential energy diagrams are used to show
the pathways that molecules take when they collide to form new products in a reaction.
These representations support the collision theory, which states that molecules are
constantly in motion and for two or more molecules to react with one another they must
collide with the correct orientation and with enough energy to overcome the activation
energy barrier. Activation energy is the extra energy needed to help the reactants form
the products and can be illustrated as a hill or a “hump.” Figure 1 shows an example of
an endothermic reaction, where more energy is needed for the reaction to occur than is
given off. Opposite that is figure 2 which shows the potential energy diagram for an
exothermic reaction. Here, less energy is needed for the reaction to occur and more
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energy is given off when the new product is formed.
Figure 1: http://www.bbc.co.uk/scotland/education/bitesize /higher/img/chemistry/calculations_1/pe_diags/fig10.gif
Figure 2: http://www.bbc.co.uk/scotland/education/bitesize/higher/img/chemistry/calculations_1/pe_diags/fig03.gif
As with many other representations in this discipline, these diagrams do have
strengths and weaknesses. An advantage of using this diagram to represent chemical
reactions is that it depicts the amount of energy needed for a reaction to occur. In
instances like this, decisions might be made as whether or not to add a catalyst to speed
up the reaction or to increase the average kinetic energy [KE] by increasing the number
of collisions by either raising the temperature, and/ or the surface area of the reactant. It
is also useful in determining whether any of the previously listed factors influenced the
reaction, such as a catalyst. In addition, this diagram can represent two types of
reactions: exo- and endothermic.
On the other hand, this diagram can become misleading by allowing observers to
visualize the molecules actually having to move over a “hump.” Also, it may appear
confusing because it does not show the effects of temperature on the reaction. Rather, the
Boltzman Distribution diagram illustrates the increase in average KE; thus, it depicts
whether temperature is a factor in the rate of the reaction.
Chemical reactions are most often associated with chemistry class. So, it was no
surprise to learn how reactions occur on a molecular level and how they are symbolically
represented. In class, we examined several different reactions using alka-seltzer tablets
and water. We observed reaction rates of crushed tablets vs. whole tablets, temperature
differences, and whole vs. half tablets. Based on those simple demonstrations, we were
able to develop the ideas that molecules are colliding to react with one another to form a
new product (CO2). From there, we discussed the uses and functions of enzymes and
how they speed up reactions by lowering the activation energy by binding to the reactants
at activation sites through the induced fit model. We even further investigated this topic
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in the lab and conducted our own investigations as to how pH affects the reaction rate.
All the while, these procedures led to an understanding of the simple diagrams listed
above.
Because energy is a fundamental scientific principle for all sciences, it relates to
other previous science classes. In particular, potential energy was discussed in detail
during our Physics I class. In a physics class, potential energy can be defined as the
energy that an object has because of its position, which is called gravitational potential
energy (Tillery, Enger, Ross, 2004). Potential energy of an object can be calculated as
the work done on an object to change its position. This correlates to the chemical
definition because the “work” done on an object is similar to the effect that a catalyst has
on substrate. Once the reactant or substrate has been catalyzed the molecules are able to
react; hence, they are changing position by colliding more frequently. Typically,
mathematical formulas are used to represent PE in the physical sense, which supports the
above statement by W.M. Goodwin. As well, cartoon diagrams are used in texts, which
use arrows to depict change of position.
In conclusion, this essay defined structural formulas and some uses in and outside
a chemistry classroom. As well, the potential energy diagram was discussed as a tool for
representing the activation energy needed during a chemical reaction. The strengths and
weaknesses of each example were outlined above. In addition, this report mentioned how
these representations are used by chemists in the theoretical understanding of the
phenomena.
Reflective Statement with Links to Other Evidence:
Original Response to Pre-Assessment:
#2:
Understanding the symbolisms and representations of the Chemistry discipline is
important because much of the calculations, structures, and formulas use symbols. For
example, understanding basic elements on the periodic table require knowledge of names
and symbols. The representation of molecules is versatile and understanding the many
different representations is important in being able to apply chemical concepts to
everyday life.
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As I think about all of the information covered throughout this Biochemistry
course, I am able to reflect upon my growth of learning. As evidenced above, my initial
understanding of EU #2 lacks detail in the explanation of the uses of symbolism and
representation in chemistry. At the time, my level of comprehension consisted of an
elementary point of view, where just the elements on the periodic table were represented
by symbols. Although, I was unable to give any other sufficient examples of how
symbolism and various representations are used throughout the discipline, I was aware
that knowing this information would be helpful with real-life applications.
Based on the above post-course essay, I feel that I have a deeper understanding
about the EU. I am able to convey several examples of symbolism and representations
and list why they are important in chemistry, discuss how specific formulas and diagrams
are used throughout, and identify the advantages and disadvantages each representation
poses. In addition, I am able to make connections across the discipline as well as across
other science curriculum and concepts. I feel I have gained a better personal
understanding of scientific principles which lay the groundwork for other concepts.
More importantly, I feel more confident in my ability to convey the information that I
have learned to my own students.
As mentioned previously, symbolism and representation relate to other scientific
principles. To demonstrate my personal growth in this area, I have chosen to include a
comparison of a homework set from Chemistry 511 and a quiz from Chemistry 512. In
both instances, I was asked to draw structures based on formulas. I was also required to
apply knowledge about valence electrons, resonance structures, formal charges, and
polarity of molecules. When observing both pieces of work, I am able to see that my lack
of understanding of structural diagrams in Chemistry 511 caused me to lose points on the
assignment. I was able to draw most structures correctly, but was vague in my
explanations of those representations. I did not back up my statements of polarity with
evidence from the structure, nor was I able to draw resonance in one instance. This
piece of evidence was one of my last assignments for that course; thus, my baseline
understanding of these representations and their uses in explaining chemical principles
was weak. In comparison, my quiz for Chemistry 512 showed a different understanding.
Using the structural condensed formula, I was able to accurately draw out representations
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properly labeled with the number of valence electrons and formal charges. As well, I
showed growth in my ability to explain these representations and symbols in terms of
evaporation rates of two separate molecules. After practice in class and at home, I was
able to relate these structures to the bonds within the molecule and how they affect the
evaporation rates for certain substances.
My second piece of evidence that I chose to show growth is my notes and quiz
corrections about activation energy illustrated on the potential energy diagram. As
evidenced in my notes and my original quiz, I had many misconceptions about the
reaction rate of molecules. I initially thought that heat/ temperature lowered the
activation energy and could be shown using a potential energy diagram. Also, I
misconstrued the collision theory and why molecules begin to “stabilize.” I originally
thought it was because they eventually stopped colliding, which of course is false because
molecules are constantly in motion. In addition, I did not have a clear understanding of
denaturation and was unable to explain the process and how it related to the diagram.
Through my reflective statements in this piece of evidence though, I was able to see why
I had difficulty with the concepts. At the time, I had not made cross-content connections
to other types of representations (i.e.: tertiary structures). Now, I am able to make those
connections for a deeper understanding of the use of these symbols and representations as
means to learn and communicate chemical principles.
Overall, I feel I have a much better understanding of this EU. I can describe
several types of symbols and representations used in Chemistry to explain molecular
concepts. These are important to the discipline because they allow us to visualize
molecular structure, shape, size, and properties. Everything in the universe is made up of
these tiny particles, called matter. Learning about them gives me a much more
comprehensive outlook on scientific world.
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References
Denniston, K., Topping, J., Caret, R. (2007). General, organic, and biochemistry.
McGraw Hill, Boston. 5th ed.
Goodwin, W.M. (2007). Structural formulas and explanation in organic chemistry
[Online version]. Foundations of Chemistry. 1389-4238
Structural formula. (n.d.). The American Heritage Stedman's Medical Dictionary.
Retrieved August 14, 2007, from Answers.com Web site:
http://www.answers.com/topic/structural-formula
Structural formulas (2005-2006). World of Chemistry. Retrieved August 14, 2007, fro,
Thomson Gale: http://www.bookrags.com/Structural_formula
Tillery, W., Enger, E., Ross, F. (2004). Integrated Science. McGraw Hill. 2nd ed. 5052.