Memorizing something essentially means changing it from something you need to think about into something you can do quickly without thinking. Sometimes this is desirable, sometimes not.
When my older daughter was 7, she understood the concept of multiplication and division. She was bored with these, and wanted to move on to more challenging concepts instead of “wasting” her time memorizing multiplication tables.
She came home from school one day saying, in a disgusted voice, “My teacher is teaching us pre-algebra. I don’t want to learn pre-algebra; I want to learn real algebra!” I taught her basic order of operations and showed her how to solve simple algebra problems, such as 3x + 7 = 19. She liked this. It was exciting, and she kept asking me to give her problems to solve. (Algebra turns out to be a great way to pass the time on long car trips!) It didn’t take her long to realize (with a little prompting) that not knowing her multiplication tables was getting in the way of solving the algebra problems and slowing her down. Within three months, she had memorized her multiplication tables up through the twelves.
I ask my students to memorize things they will need often and won’t want to waste time looking up. I don’t ask them to memorize anything that they’re unlikely to need often. (They’re often amazed at the number of elements for which I’ve memorized the average atomic mass. This turns to amusement after the moles & stoichiometry topic, when I point out to them that they’ve managed to retain the atomic masses for carbon, hydrogen, oxygen and nitrogen without even trying.)
Here are most of the formulas/relationships that I specifically ask them to memorize. (There are probably a few others I’m failing to think of at the moment, but not a lot.)
- location, symbol, name, and charge of ion for elements in groups 1 & 2
- location, symbol, name, and charge of negative ion for most nonmetals
- location, symbol, and name of some other common metals
- formulas and charges of about a dozen common polyatomic ions
- ideal gas law
- common pressure units (so they can recognize them in word problems)
- units for commonly used quantities, such as mol/L, g/mol
- value of the gas constant (8.31 J/mol K), because it appears in so many different contexts
- ΔG = ΔH – TΔS
- how to write an equilibrium expression
- Coulomb’s Law
I specifically ask them not to memorize sequences of steps for solving problems, such as mass-mass stoichiometry problems and dilution problems, because I want them thinking about what’s actually going on in these problems rather than blindly following a procedure.
I do the same thing in the lab. I give my students a specific objective, a general overview of what the procedure will look like (as a demo plus a brief opportunity to practice any necessary techniques), and a specific list of what I’m looking for in the analysis. In the lab, they need to use the objective, overview, and techniques to work out the details of the procedure in their lab groups, write down the procedure as they perform it, and take the data necessary to perform the required analysis. Since I started doing labs this way, I’ve gotten a much higher level of retention and understanding of what they were doing in the lab, why they were doing it, how well it worked, and how it relates to what they’ve learned in the classroom.
Originally posted to the ChemEd-L discussion list.
