electron+configurations

Writing electron configurations will require the use of a periodic table, and an understanding of how energy levels and sublevels are laid out on the table. Refer to the following diagram for this information. Recall that energy levels are the horizontal rows, and sublevels are the four main blocks of the table (colored for you here).



To determine an element's electron address (think location) using the periodic table as a map, follow these steps: 1. Find the energy level (horizontal row number) for the element; 2. Find its sublevel (letters s, p, d, or f); 3. Count the number of columns over within that sublevel to determine how many electrons it has in that sublevel.

1. Sulfur is in the third horizontal row from the top, so its energy level is **3**. 2. Sulfur is in the p sublevel (green in the table above), so write **3p**. 3. Finally, sulfur is the fourth one over in the p sublevel, so its electron address is **3p** 4. (Note: the number of electrons is superscript, like an exponent.)
 * Example: sulfur**

So sulfur's electron address will end at 3p 4. But it has 16 electrons, so we can't just write 3p 4. Electron configurations always go in order from the nucleus outward towards the valence shell (outermost set of electrons).

Every element's electron configuration starts at the top left with hydrogen, and builds left to right and down until you reach the position of the element in question. Think of it as starting from the nucleus of the atom and taking the elevator through each 'floor' of that atom's electron layers.



When writing an electron configuration for an element, always start at 1s and work your way up the energy levels.

So with sulfur, we have to start at hydrogen, and then work our way through (follow the atomic number) to sulfur.

Each of the inner (core) sublevels will be filled, so be aware that the s sublevel can hold at most 2 electrons; p can hold up to 6 electrons; d can hold up to 10 electrons; and f sublevels can hold up to 14 electrons. This is due to the number of orbitals in each sublevel, and one orbital can hold two electrons.

Again, for sulfur, we need:

1s 2, 2s 2 , 2p 6 , 3s 2 , then 3p 4. That's the electron configuration for sulfur.

Here is another good visual:

And one more:

Now look at tungsten for another example. Its symbol is W, and atomic number is 74. We need to show 74 electrons in its address!

So, start at #1 and follow the organization of the periodic table through the atomic numbers:

1s 2, 2s 2 , 2p 6 , 3s 2 , 3p 6 , 4s 2 , 3d 10 , 4p 6 , 5s 2 , 4d 10 , 5p 6 , 6s 2 (Ok, here it gets interesting. Just follow the atomic numbers.)... 4f 14 , 5d 4 and that gets you to tungsten!