After almost 40 years as a Chemistry teacher, I have noticed that the prescribed order of topics in high school chemistry is, according to the Province of Ontario’s Guidelines, anywhere from less-than-ideal to downright illogical. Students are frequently asked to study topics in a manner that requires memorization at the expense of conceptual understanding. This results in less-than-optimal student understanding and less-than-optimal student learning. Simply put, illogical sequencing makes things difficult for everyone. Teachers have a tough time forcing students to “learn” concepts for which they have not been prepared; students must cram largely meaningless information into their heads.
When concepts are taught in a logical order that emphasizes the foundational, empirical nature of the discipline, students gain understanding. A random, ill-thought-out order of topics demands—and relies on—memorization. A prime example of illogical sequencing can be found in the International Baccalaureate (IB) Chemistry program, Standard Level (SL). IB asks students to understand the electronic nature of benzene before teaching orbital hybridization. How can students be expected to understand delocalized electrons without first understanding hybridization? Are students simply to memorize sp2 hybridized carbon atoms and the resonance concept? Where is the sense?
As for labs, it is my humble opinion that they should, whenever possible, be completed before a topic is taught. This pays homage to the empirically driven nature of chemistry. Empirical observations drive the modeling, not vice versa. I start Honors Chemistry with a simple, accurate experiment to determine the relative atomic mass of Mg : Zn. Students begin the course by carrying out single displacement reactions, using water displacement to collect a gas quantitatively, and they learn something about the periodic table. What a great way to begin the formal study of chemistry: by DOING chemistry to obtain a fabulous result that explains, at least a sliver, of the Periodic Table. You can read more on these ideas in my post, The Soft Introduction.
When students study the polarity of simple, octet guideline-compliant molecules in Honors Chemistry, they should begin with empirical evidence in the form of a solubility “like dissolves like” lab or a set of teacher demonstrations to illustrate the same. This provides an empirical foundation. To explain solubility observations, students must be equipped with VSEPR Theory. This affords a 3-D picture of simple molecules. Combined with qualitative vector addition, students can now understand the polarity/non-polarity of simple molecules. (See supporting information for VSEPR theory notes.)
Significant figures and measurements should be taught immediately before students begin quantitative work, not as a stand-alone at the beginning of a course, to be re-visited a month or two later. This super-important topic is best introduced empirically before proceeding to the theory.
You can also introduce Hess’s Law of heat summation empirically. If students are familiar with using a coffee cup calorimeter, let them do the lab first. If you are concerned that student data won’t be accurate enough to illustrate Hess’s Law, you could provide raw data for a “dry lab” up front. Students can complete the calculations that exemplify Hess’s Law using the provided data. Your class could always do the “real” experiment later.
And so on . . .
Additionally, when the sequencing of topics is logical, opportunities for review continually present themselves. For example, these concepts can be applied logically to subsequent topics when the oxidation number concept (and oxidation-reduction reactions) are taught early on based on Lewis structures and electronegativity. In the chromate-dichromate equilibrium, studied as part of LeChâtelier’s Principle, students can be asked to determine the oxidation number of chromium in the dichromate ion, Cr2O72–. This is a tiny question; it takes under a minute to ask and answer, but it makes for a built-in review.
This review method, done daily, eliminates—or reduces—the need for gigantic end-of-course reviews, which occur at the expense of teaching time and lab time.
The following is my chronological topic sequence for two years of high school chemistry: Honors/11 Chemistry and 12/AP Chemistry.
Honors Chemistry
- Chemical Reactions
- History of the Atom/Atomic Theory
- Significant Figures and Measurement
- Mole and Molar Relationships
- Solution Chemistry
- Acids and Bases
- Gases
AP Chemistry
- Oxidation Number Concept, Redox Reactions, Balancing Redox Equations
- Structure of Matter/Atomic Theory and Bonding
- Thermochemistry
- Rates of Reaction
- Chemical Equilibrium and Applications
- Electrochemistry
- “Big Picture” of Physical Chemistry
- Organic Chemistry (after AP Exam, if desired/necessary)
I have separated the oxidation number concept from electrochemistry to make for a “full circle” experience. Since electrochemistry ties in—directly or indirectly—with so many concepts, this makes for a fulsome review that provides a “big picture” of much of the physical chemistry part of high school chemistry.
The following is the final slide that I use in AP Chemistry. Students report a gratifying “ah-ha” moment when they see how everything “fits.”
Take a look:
Teachers are responsible for the learning outcomes of their students. Therefore, it makes sense that teachers MUST take the necessary liberties when it comes to topic sequencing.
Chemistry Education is too important to leave to the “experts.”
