Electron Configurations
In 1911 Rutherford proposed our present view of the nuclear atom. His model described the atom as having a very
small nucleus containing most of the mass and all of the atom’s positive charge. Bohr proposed that negatively
charged electrons were distributed around the nucleus at great distances giving an atom a volume which was mostly
empty space.
Schrodinger developed a theory describing the most likely location of electrons around the atom. Using the results
of this theory, a method was developed for writing electron configurations. Whole numbers 1,2,3, and so on, are
used to denote the main energy levels, and s, p, d, f, denote energy sublevels. Superscripts above the sublevel letter
indicate the number of electrons in that sublevel. For example 2p4 indicates 4 electrons in the p sublevel of the
second energy level. The electron configuration for oxygen would be 1s 22s22p4. The details on the order of filling
and energy level capacities are given in your text and should be in your notes.
Orbital filling diagrams also illustrate the distribution of electrons. For our purposes you only need to draw the parts
of the orbital filling diagram which include the valence electrons only. Oxygen’s orbital filling diagram would be:
2s
2px
2py
2pz
Note that the electrons in the same energy level do not pair until each orbital is occupied with one electron, in
accordance with Hund’s rule.
A third method used to show electron arrangement is the Lewis Dot Diagram This notation uses only those s and p
electrons in the highest energy level. The s and p orbitals are arranged around the element symbol for the element.
The Lewis Dot Diagram for oxygen is shown to the right
.
.O:
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Each of these methods for representing electron has merits, and they can be used to illustrate the concepts of
bonding and molecular structure. In this exercise, you will practice each method of illustrating electron distribution.
Procedure:
1. Create a table on a separate sheet of paper in landscape orientation. The table should include a column for
element symbol, electron configuration, orbital filling diagram, Lewis Dot diagram, valence and ion charge
(oxidation number).
2. Fill in the table for each of the following elements:
a. sodium, Na
i) Cobalt, Co
b. tungsten, W
j) technetium, Tc
c. arsenic, As
k) gallium, Ga
d. strontium, Sr
l) silicon, Si
e. gold, Au
m) samarium, Sm
f. nitrogen, N
n) sulfur, S
g. iodine, I
o) radium, Ra
h. thorium, Th
p) ruthenium, Ru
Questions:
1. The orbital filling diagram has arrows pointing in opposite directions when two electrons occupy the same
orbital. What do these arrows indicate? Why do they have a direction to them?
2. How many electrons do the elements in group 2 of the periodic table have in their Lewis dot diagrams?
3. Element X has the following electron dot diagram:
Name all the known elements that could have this dot diagram.
.
4. What element has 4 electrons in its highest energy level
.X:
5, with 2 in the s sublevel and 2 in the p sublevel.
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