Chemistry Reference
In-Depth Information
Step 2. Determine the number of electrons for the specific element.
A.
If the atom is neutral, then the number of electrons is equal to the number
of protons. Because no charge was mentioned, we know that this is
a neutral atom. So, the number of electrons = 13.
Step 3. Consult the arrow diagram to determine the order in which the sublevels
should be filled. We look at the arrow diagram, and we see the order in
which the sublevels are cut by the arrows. We start with the tail of the
top arrow, and trace it to the tip. When you get to the tip of an arrow,
you proceed to the tail of the next arrow down. It begins with 1s, then
2s, then 2p, 3s, 3p, 4s, 3d, and so forth. We won't need to fill all of these
sublevels, but we need to be able to read the order.
Step 4. Write the configuration, filling in up to 2 electrons in each “s” sublevel,
up to 6 electrons in each “p” sublevel, up to 10 electrons in each “d” sub-
level, and up to 14 electrons in each “f” sublevel. We have 1s
2
2s
2
2p
6
3s
2
3p
1
, and that brings us up to 13 electrons.
Step 5. When you think that you are finished, add up the exponents (super-
scripts) to see if you have the correct number of electrons. Adding the ex-
ponents of 1s
2
2s
2
2p
6
3s
2
3p
1
(2 + 2 + 6 + 2 + 1), we get 13 electrons, so
our configuration is probably correct.
The full electron configuration for the element aluminum (Al):
1s
2
2s
2
2p
6
3s
2
3p
1
Were you surprised that we only placed 1 electron in the 3p sublevel?
Remember that when we say that a “p” sublevel can hold up to 6 electrons,
we mean that 6 is the maximum that it can hold. In this case, we only had to
place 1 electron in the final “p” sublevel to get up to 13 total electrons.
Can you figure out what the shorthand notation would be for the ele-
ment aluminum? Notice that its kernel configuration is identical to the
configuration we did for neon, in Example 1. The shorthand notation for
aluminum is shown here:
The Shorthand Electron Configuration of Aluminum
[Ne]
3s
2
3p
1
For our last example, let's try an example of an atom that has obtained
a charge, which, as you know, is called an ion.
