Chemistry: The Aufbau and The Pauli Principles
Continuing from the last chemistry post, I have found it so much easier to explain the Pauli Principle and the Aufbau Principle by using a visual model of the atom.
The electron configuration of Cl (Chlorine) [Ne] 3s2,3p5.
This manipulative is part of the Friendly Chemistry program. It is a plastic coated page that fits snugly inside a baking pan. Small magnet discs in two colors are used to represent the electrons, one color representing the electrons moving clockwise, and the other color representing the electrons that move counter-clockwise.
I have made similar manipulatives with posterboard before in a co-op class, however, with success. Once I hot glue-gunned tiny bathroom cups to the circles and then used small pom-poms in two colors to be placed in the cups to represent the electrons, although the even smaller cups found in some restaurants or fast-food places would work even better, if you can get enough of them.
I have also just made the circles on posterboard or large sheets of construction paper and used math counters or glass discs that are sometimes used with planters, which can be found in the garden section or sometimes in dollar stores, without the cups. You just have to be careful that the paper doesn't get knocked.
Whatever method you use, you just start with the nucleus of the atom at the bottom and using the Aufbau principle, make the appropriate circles representing the possible orbitals to be filled.
Aufbau principle: The orbitals are filled in the order 1s, 2s,2p,3s,3p,4s,3d,4p,5s,4d, 5p, 6s, 4f, 5d, 6p, and so on.
The electron configuration of C (Carbon) [He] 2s2, 2p2.
Once you get your board set up, your student can begin filling the circles, using the Pauli principle. Don't forget that when your student gets to atoms which need to fill the x, y and z orbitals of the 2p, for example, that he must add the first electron to either the x, y or z orbital and then whichever one he chooses, the other two p orbitals must be filled before adding a second electron to those set of three orbitals.
The Pauli principle: Each orbital can hold at most hold two electrons.
We also looked at the fact that each atom has the configuration of the nearest previous noble gas atom, which is in brackets, and whatever valence electrons it has, which is listed after.
For example, in this visualization, this is the configuration for of Cl (Chlorine) is its nearest previous noble gas atom, which is [Ne] or Neon and then also has the valence electrons of 3s2,3p5. Once your student can easily place these electrons, then you can easily teach them about the differences between ionic and covalent bonding.
