Untitled - Kelly Walsh High School

Quantum Theory and Electrons 113
Don’t Forget!
There are several ways of indicating the arrangement of the electrons in an
atom. The most common way is the electron configuration. The electron configuration
requires the use of the n and l quantum numbers along with the number
of electrons. The principle quantum number, n, is represented by an integer
(1, 2, 3 . . . ), and a letter represents the l quantum number (0 s, 1 p, 2 d,
and 3 f). Any s-subshell can hold a maximum of two electrons, any p-subshell
can hold up to six electrons, any d-subshell can hold a maximum of 10 electrons,
and any f-subshell can hold up to 14 electrons.
For example, lithium has three electrons, two in the 1s-orbital and one in the 2s
orbital. Its electron configuration would be: 1s 2 2s 1
The sum of the superscripts must equal the total number of electrons present.
The electron configuration for fluorine (nine electrons) is: 1s 2 2s 2 2p 5 . Figure 7-2
shows one way of remembering the pattern for filling the atomic orbitals. (Your
text/instructor may present an alternate way of representing this pattern. Learn
the one that makes the most sense to you.) The filling begins at the top of the
pattern and follows the first arrow. When you reach the end of the first arrow,
you go to the second arrow and follow it to the end. The third arrow continues
the pattern, and so forth.
Figure 7-2 One method of remembering
the pattern for filling the
atomic orbitals (Aufbau principle)
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
7p
3d
4d
5d
6d
4f
5f