Chemistry Reference
In-Depth Information
Next, we will draw one circle for each orbital. Remember from the last
lesson that “s” sublevels contain 1 orbital (as shown in Figure 3-4e on page
89), “p” sublevels contain 3, and the “d” and “f” sublevels hold 5 and 7
orbitals, respectively.
1s
2
2s
2
2p
6
3s
2
3p
1
Now, if you choose to represent the electrons by arrows, you put one
arrow in the orbitals with only one electron and two arrows in the orbitals
with two electrons, as shown below. Remember: An electron can only hold
up to two electrons, so there will never be more than two arrows in a circle.
1s
2
2s
2
2p
6
3s
2
3p
1
Notice that you will not always fill in all of the circles that you draw.
Aluminum only has one electron in the 3p sublevel, so only a single 3p
orbital has an electron. For our next example, let's try an orbital notation
in which Hund's Rule becomes more important.
Example 2
Write the proper orbital notation for an atom of phosphorus.
We start be looking up the atomic number for phosphorus, which is 15.
We then do the electron configuration for the element, based on the rules
that we learned early in this chapter, and find it to be 1s
2
2s
2
2p
6
3s
2
3p
3
. We
space our electron configuration out, to make room for the circles repre-
senting our orbitals, and fill in the arrows to represent the electrons, as
shown here.
1s
2
2s
2
2p
6
3s
2
3p
3
Do you see how we apply Hund's Rule? The atom is more stable if it
has more electrons with parallel spin, so we place one electron in each of
the 3p orbitals, rather than putting, say, two electrons in the first orbital
and one in the second. It is easy to remember what to do: When you are
filling the orbitals within a sublevel, each orbital gets one electron before
