Electron Configurations

So today in class we had quite a long, and somewhat decieving, lecture by Mr. Lieberman.

We learned how to find the electron configurations for neutral elements. The first sublevel s can only hold two electrons, therefore, if the electron is completely filled at this level, the equation would read: 1s^2. The superscript (or exponent) tells you the element. Since the exponent is 2, the element would be Helium. Once a sublevel has been completely filled, if another electron is added, then a new sublevel begins to fill. If this sublevel is completely filled, then the equation would read, 2s^2. Now, this is where it gets tricky. In order to be able to identify the element, you must add this exponent to the exponent in the previous sublevel(s). In this case, 2 from the first sublevel and 2 from the second sublevel gives you 4 electrons. Now you are able to identify the element, which would be Beryllium. Energy sublevels continue to be filled and you add the exponents the same way to find the element.

A further explanation from the book might help you understand this.

1. The elements in groups 1 and 2 on the Periodic Table are filling an s sublevel. Thus, Li and Be in the second period fill the 2s sublevel. Na and Mg in the third period fill the 3s sublevel and so on.


2. The elements in groups 13 through 18 (six elements in each period) fill p sublevels, which have a capacity of six electrons. In the second period, the 2p sublevel starts to fill with B and is completed with Ne. In the third period, the elements Al through Ar fill the 3p sublevel.


3. The transition metals, in the center of the periodic table, fill d sublevels. Remember that a d sublevel can hold ten electrons. In the fourth period, the ten elements Sc through Zn fill the 3d sublevel. In the fifth period, the 4d sublevel is filled by the elements Y through Cd. The ten transition metals in the sixth period fill the 5d sublevel. Elements 103 to 112 in the seventh period are believed to be filling the 6d sublevel.


4. The two sets of 14 elements listed separately at the bottom of the table are filling f siblevels with a principle quantum number two less than the period number. That is... 14 elements in the sixth period (elements 57 to 70) are filling the 4f sublevel.

An example of an equation we did in class is as follows:

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5p^2 6s^2 4f^14 5d^10 6p^6

The subscripts tell you the energy level, the letters tell you the orbitals, and the exponents (or superscripts), when added together, tell you the electrons. If you were to add all the exponents in this equation, the number would be 86, which is the element Rn (radon).

The next scribe is...

Matt B.