ALEKS Alex H. Yuan - 09/08/2014 10:03:42 AM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
9/8/14 10:05 AM
Alex H. Yuan - 09/08/2014 10:03:42 AM EDT
General Chemistry (First Semester) / Chem 110 FA 2014 – CH110 FA14 S25-36 (Dr.
Barber)
1.
Drawing a box diagram of the electron configuration of an atom
Draw the electron configuration for a neutral atom of argon.
The electron configuration of an atom is the arrangement of electrons in it. Specifically, an
electron configuration is the set of quantum states to which an electron has been
assigned.
One way to describe an electron configuration is with a box diagram, which is what you've
been asked to draw in this problem. Here's an example of a box diagram:
The electron configuration of a neutral atom of
fluorine.
Here are the key facts about a box diagram you need to know.
Each orbital is represented by a box. Orbitals in the same subshell are grouped
together and given one label. For example, in the diagram above the three orbitals
in the
subshell are grouped together.
Each electron is represented by a half-headed arrow. In the diagram above, there
are arrows for the electrons in a neutral atom of fluorine.
Each electron arrow can point up or down, depending on the spin angular
momentum number
of the state the electron is in. Usually we imagine the "spin
up" arrow corresponds to
and the "spin down" arrow to
Very important: the Pauli Principle tells us that no two electrons can be in the same
quantum state. That means each orbital can hold only two electrons, one with spin
https://secure.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lJ…UP--TvWqiTe5EZmq7Giwnjw8YO0KzoP7zn3FzqHwK0M1_FZ00ttIGnIWv6l1c1sHT
Page 1 of 4
ALEKS Alex H. Yuan - 09/08/2014 10:03:42 AM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
9/8/14 10:05 AM
up and one with spin down.
The boxes are sometimes arranged so that their height tells you the relative energy
of the subshells. For example, in the diagram above you can see that the
boxes
are drawn higher than the
box, because the energy of an electron in the
subshell is higher than the energy of an electron in the
subshell.
You can draw a box diagram for any atom by using the aufbau principle.
The aufbau method says the electron configuration of an atom can be built up by
adding electrons to orbitals in order of increasing orbital energy. ("Aufbau" is
German for "building up")
Here's how to use the aufbau method:
Count the total number of electrons in the atom. Do this very carefully. Remember, if
you make a careless mistake in this first step, all your subsequent work will be
useless.
Imagine the possible subshells in order of increasing energy. You may find it helpful
to draw a chart in which the possible subshells are listed with increasing up the
rows and increasing to the right along the columns. The
rules tell you that
the subshells increase in energy as you go along the upward diagonals of this chart,
like so:
In this chart, the
energy of the subshell
increases along the
upward diagonal
arrows.
Drag the slider with
your mouse to see the
first subshells
highlighted in order of
increasing energy.
Begin drawing boxes and filling them with electron arrows. Begin by drawing a box
for the lowest-energy orbital, the
orbital. Put one electron arrow in it, if you are
https://secure.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lJ…UP--TvWqiTe5EZmq7Giwnjw8YO0KzoP7zn3FzqHwK0M1_FZ00ttIGnIWv6l1c1sHT
Page 2 of 4
ALEKS Alex H. Yuan - 09/08/2014 10:03:42 AM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
9/8/14 10:05 AM
drawing the diagram for hydrogen. Otherwise, put two electron arrows in it, one up
and one down.
Continue adding boxes in order of increasing energy, and putting arrows into them
until you've written as many arrows as you have electrons.
Add boxes in groups corresponding to all the orbitals in a subshell. For example,
add three boxes when you add the
subshell. Add five boxes when you add the
subshell.
Draw the boxes for each new subshell a little higher than the boxes for the previous
(lower energy) subshell.
Make sure you put no more than two electrons in each box, and make sure the
arrows are paired, up with down. If you have only one arrow, you can draw it up or
down, although traditionally most chemists draw solitary arrows up.
Important: when you don't have enough electrons to fill all the orbitals of a subshell, you
must use Hund's Rule to decide how to distribute the electrons.
Hund's Rule: when the orbitals in a subshell are not filled with electrons, the
electrons are as spread out as evenly as possible among the orbitals.
For example, there are two ways to draw the electron configuration of a carbon atom, but
only one follows Hund's Rule:
This diagram for carbon is WRONG, because the
This diagram for carbon
electrons in the
subshell are not spread out
follows Hund's Rule.
as evenly as possible.
Here is the completed electron configuration diagram for a neutral atom of argon:
https://secure.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lJ…UP--TvWqiTe5EZmq7Giwnjw8YO0KzoP7zn3FzqHwK0M1_FZ00ttIGnIWv6l1c1sHT
Page 3 of 4
ALEKS Alex H. Yuan - 09/08/2014 10:03:42 AM EDT - Copyright © 2014 UC Regents and ALEKS Corporation
9/8/14 10:05 AM
Copyright © 2014 UC Regents and ALEKS Corporation
https://secure.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lJ…UP--TvWqiTe5EZmq7Giwnjw8YO0KzoP7zn3FzqHwK0M1_FZ00ttIGnIWv6l1c1sHT
Page 4 of 4