they’re in the s area of row 2 and fill the 2s subshell and keep going.
Starting with boron (B) and continuing through fluorine (F), we are in the p
area of row 2. Boron atoms have 1 electron in the 2p subshell, carbon atoms
have 2, and so on—up to fluorine, which has 5 electrons in its 2p subshell.
Step 4. This makes the electron configuration of a fluorine atom
1 s^22 s^22 p^5 . The superscripts indicate the number of electrons occupying a
particular subshell. Adding these superscripts gives the total number of
electrons in a species. Since fluorine has the atomic number 9, we expect
fluorine atoms to have 9 electrons.Check Your Work
Add the superscripts
from fluorine’s electron
configuration: 2 + 2 + 5 = 9.
This can serve as a check
of your work or as a quick
way to eliminate incorrect
choices on an electron
configuration question.Finding the electron configuration of ions follows the same rules as those for
atoms but with one additional step. Suppose we need the electron configuration
of the fluoride ion, F−. First, find the electron configuration for the atom. That
would be 1s^22 s^22 p^5 . Now, how does F− differ from the neutral F atom? It has 1
extra electron. So add 1 electron to the electron configuration. Thus, the electron
configuration of F− is 1s^22 s^22 p^6 (the same as that of a neon atom). If we were
dealing with positive ions, we would find the atomic electron configuration and
then remove one or more electrons.
Now, what about the f subshell, which you might remember learning about in
school? For the test you don’t have to know much about it. Just remember this:
If an element has an atomic number greater than 57, some of its electrons are in
the f subshell, which is another way of saying they’re in f orbitals. So, element
number 76, osmium (Os), has electrons in the f subshell, as do gold (Au),
samarium (Sm), and terbium (Tb).
One more thing: The Aufbau principle states that a subshell is completely filled
before electrons are placed in the next higher subshell. But there are some
exceptions to this principle that are worth mentioning. First, since completely
filled and half-filled d subshells give extra stability to an atom, chromium (Cr)
and copper (Cu) violate the Aufbau principle and promote a 4s electron to the 3d