Periodic Table Organization Projects

One of the goals of scientific chemistry teaching is to get the students to retain the information, rather than have it be an "in one ear, out the other once the exam is over" trivia lesson. To do this, projects covering material should focus on the interrelation of the material rather than memorizing numbers, facts and figures. One example of this sort of teaching methodology is a periodic table organization project.

Development of Periodic Table

Dmitri Mendeleev organized a catalog of all the elements known to science circa the 1860s in a table, grouping elements in columns together based on their chemical properties and reactivity, and his work built off of the groupings of elements into triads by German chemist Dobereiner, who'd noticed similar properties among iodine, bromine and chlorine. As more information on atomic weights became known, Mendeleev sorted the elements onto cards and arranged them in rows in ascending atomic weights, but tried to keep columns of similarly reactive elements together. This is why he put tellurium before iodine in his draft of the table.

What's Happening With Elements?

What is known now that Mendeleev did not is the subatomic structure of the elements, which are made up of protons, neutrons and electrons. Chemical reactivity is largely a function of the number of electrons in the outermost shell of the element; the inner shell can hold two electrons, while the next shell can hold eight (resulting in lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon). As the outer electron shells fill, the elements become less reactive.

Electron Shells

To demonstrate what's going on with electron shells, it's useful to get a peg-board and some pegs. This is really only practical to the second or third row of the periodic table, but it demonstrates what's going on nicely. Make some diagrams that show the number of "open electrons" in each level of the electron shell--it's easiest to start with the noble gases, which will have a full shell of two electrons (helium), eight electrons (neon) and eight electrons (argon). Then work backward from that column and remove one additional peg from each element going back. Now, have your students play "mix and match"--why don't the noble gases react that much? Because they don't have any places where other elements can grab onto them. Why do the alkali metals react most readily with everything? Because they all have one extra electron sticking out to act as a key into any reaction hole available.

Nuclear Compounds

The next activity can also work (at least for the first three rows) by helping students build "atomic weights" through putting a count of how many protons and neutrons are in each atomic nucleus; there is less periodicity with this than there is in electron shells because neutrons aren't as reactive, but it also opens the door to discussing isotopes of elements and gives your students a way to visually put together the information on how atomic mass varies.