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Boston Tutor Charles Robinson, Ph.D.
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  Tutor   >    Boston Chemistry Tutor

Boston Chemistry Tutoring

My two decades of experience as a chemistry tutor has lead me to become particularly creative when it comes to tutoring chemistry.  General chemistry and organic chemistry can both be approached as Lego games.

I have asked many students, "Did you play with Lego when you were young?"  The answer is almost always, "Yes!" and it usually seems to be a happy memory.  My unique approach makes the chemistry learning experience a positive one while improving the student's skills.

I teach chemistry, at all educational levels, as a Lego game played with a weighing scale.  The weighing scale takes the student through stoichiometry.

We carefully note the areas where chemistry departs from a simple Lego game.  We also note the different Lego games.  One Lego set consists of only three kinds of Legos (proton, neutron, and electron), which you snap together to make up the periodic table of elements.  The second Lego set is the periodic table of elements, which you snap together to make molecules.

Lewis Diagrams

Another part of my chemistry tutoring is to use the concept of Lego sets to make Lewis diagrams.  I notice that some students have trouble with Lewis diagrams.  I think it's because it is never stated exactly what the Legos are.

The Lewis diagram for carbon dioxide is ::O::C::O::.  (The first 2 pairs of electrons to the left of the first 'O' should be written as separate pairs, as should the last 2 pairs of electrons after the second 'O'.  And the last dot is meant to be a period, rather than an electron.)

What are the Legos here?  The answer is that 'O' stands for an oxygen atom stripped of its valence electrons.  In other words, the 'O' stands for the oxygen nucleus plus two inner shell electrons.  Put another way, the 'O' symbol stands for a Lego that has a net charge of +6.

No such species exists in nature (any more than a Lego kit of protons exists in nature), but it does exist in our mind when we draw Lewis diagrams, if we are to understand those diagrams correctly.

The 'C' stands for the carbon nucleus together with two inner-shell electrons, and thus has charge 4.  Of course the dots stand for electrons.

Now we can do the simple arithmetic on the charge of the carbon dioxide molecule shown in the Lewis diagram: Two charge-6 'O's and one charge-4 'C' (which makes charge +16), and 16 electrons, which makes for a charge-0 molecule.

So the Lego pieces in Lewis diagrams are of two kinds: (1) Positively charged species consisting of an atom stripped of its valence electrons and (2) electrons.  As obvious as this is, I find that making it explicit takes the mystery and difficulty out of Lewis diagrams for many students.

Several different Lego games

At each stage of one's studies in chemistry, it is important to make explicit what is the exact nature of the Lego game, or model, that is being employed.  It is necessary also to make explicit where the model departs from a simple Lego model.  By providing this knowledge, I am able, when teaching chemistry, to maintain my conviction, and convey to the student the conviction, that chemistry is really rather an easy subject to understand.

This approach works in a first year general chemistry course, for areas from stoichiometry to electrochemistry, and it works as well for understanding SN1 and SN2 reactions in organic chemistry.

The Weighing Scale

Our chemical lego game is played with a weighing scale.  If a bagel weighs one tenth of a pound, how many bagels in a pound?  Most students understand that the answer is ten.

So if a proton weighs one six hundred hextillionth of a gram, how many protons in a gram?  In the same manner as with the bagels, the answer is six hundred hextillion.  This is Avogadro's number.  Suddenly the student understands why Avogadro's number is what it is, and what it means.  Suddenly the student understands what a mole is and how it works.  A mole of oxygen atoms weights 16 grams, not by magic or because the book says so, but because we understand how to use our (imaginary) weighing scale.

Chemistry is Easy

In summary, the basic idea behind the way I teach chemistry to individuals is that I convey and support the conviction that chemistry is easy.

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