Alternative Presentation for Radius Cake Activity found in Lesson 10

Items you'll need:

-batch of homemade playdough (link to recipe is below)

-copy of periodic table made on regular copy paper

-uncooked spaghetti noodles (a one-pound box is enough for 20+ students)


Instead of making a cake to build your 3-dimensional graph of the atomic radii of elements 1-49, we suggest you make a base of playdough.  

The making of the playdough can be done by your students or by you before your class begins.  We used 1 batch of dough per student, but this could be done in groups or as a demonstration.   One batch per student is ideal.

 There are many available recipes for making homemade playdough.  Here is a link to a microwave method we used which worked very well:

This same recipe can also be made on a stovetop surface.  The key to success is the necessary stirring as the mixture heats.  Either way you make it, microwave or stovetop, the dough will be hot once it forms into a ball.  Caution should be taken not to get burned.  Coloring the dough is not necessary, but doing so can make it more fun or useful for other activities.  We used food coloring but koolaid works, too.

Once the dough is prepared and cooled, knead it on wax paper into a soft mass.  Then flatten it into a rectangle about the size of an 8.5 x 11 inch sheet of paper.  Keeping it on the wax paper can make clean-up easier.  The dough will end up being about 1/2 inch thick.

Now that your dough is ready, you'll need copies of a periodic table.  Any in the textbook will work.  You'll need one copy per batch of dough.  We found that pre-punching a small hole in each element square on the periodic table makes insertion of the spaghetti pieces, done later, much easier.  Creating these holes can be done with the point of a pencil or pen.  It doesn't really matter where in the square you punch the hole, just being consistent from square to square helps keep things orderly.

Next, lay the copy of the periodic table across the flattened dough.  We found the paper to stay put by pressing the periodic table into the dough.  If you find the paper to move around, you can anchor the corners into the dough by inserting short pieces of spaghetti through the paper into the dough.

By referring to the atomic radius chart in the book, have your students break sections of the uncooked spaghetti noodles into lengths representing  the radius of each element.  Note that it's the relative amounts which are important; we're trying to see trends in sizes and being exact in measurements is not really necessary (unless of course, that's an objective you might have with your students!)

As your students continue inserting the spaghetti pieces, they should begin to see how the radius of atoms of elements vary as one goes "down" a family of elements and then "across" a series or period of elements.  We found the spaghetti to work very well, better than toothpicks!

See students in action here on youtube:

Advantages to this approach:

-you don't have to "create" a periodic table on top of the playdough, just use a printed copy.

-you can re-use the playdough again later (bag and refrigerate.)  With some classes in the past, we made playdough earlier in the course when discussing atomic numbers and made little models of atoms with appropriate numbers of subatomic particles.  These were just temporary models as we balled up the dough and then stored in the fridge.

-you can utilize the process of making the playdough as a lab, too.  (Practicing measurement skills, following a procedure, clean up skills.)

-slightly less messy to prepare and then easier to transport once prepared if you have to travel to class site.


-you can't eat the playdough when you're done like you can when using cake.  I've heard of some folks using a pudding base, but the periodic table has to be frosted on or done with Twizzlers etc.

-requires microwave oven or stovetop.  Even though the microwave makes the playdough faster than the stovetop, 3-4 minutes for 10 students does end up taking almost an hour, so you may need to be prepared for that or just make it beforehand.  

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