Chemistry Reference
In-Depth Information
1
18
1
2
3
4
5
6
7
2
3 4 5 6 7
Be
Si
3456789012
Fe
Rb
Figure 3-7e
beryllium is “2s
2
.” When we construct the full electron configuration as de-
scribed in Lesson 3-4, we find that beryllium, which has an atomic number
(often represented by the symbol “Z”) of 4, shows the configuration: 1s
2
2s
2
.
Do you see how we can check the configuration using the periodic table?
Let's look at the element rubidium (Rb) next. What can we tell from its
position on the periodic table? It is in the fifth period (horizontal row), and
in the first column of the “s” section of the periodic table. This tells us that
the valence configuration of rubidium must end in 5s
1
. When we construct
the full electron configuration of rubidium, with its 37 electrons, we get 1s
2
2s
2
2p
6
3s
2
3p
6
4s
2
3d
10
4p
6
5s
1
. Again, our resultant configuration matches
our predictions.
Iron (Fe) is slightly trickier, because it is located in the “d” section of
the periodic table. The trick to the “d” section of the periodic table is that
the valence shell of these elements is not made up of “d” electrons. Re-
member that there are only up to 8 electrons in the valence shell, which is
why only 8 electrons can
fit around the Lewis dot
notation of any given el-
ement. Refer to Figure
3-7f to refresh your
memory.
You see, the “d”
sublevels can hold up to
10 electrons, and there
is no room for them on the Lewis dot notation. This means that when you
are filling up a “d” sublevel, you are not filling up the valence shell. How is
that possible? The answer can be found by looking once more at the arrow
diagram.
Lewis Dot Notation
s orbital
p orbitals
p1
p3
s
p2
elemental symbol
Figure 3-7f
