Lesson 6: Electronic Configuration Notation
As we mentioned earlier, the electronic configuration notation (which is the second of three notations you will learn)
builds upon the skills you acquired in learning the orbital notation. In orbital notation you used arrows to designate the
electrons found in each orbit. In electronic configuration notation (ECN), you will replace those arrows with superscripts
(small numbers written above the orbit notations, also known in math classes as "powers"). As we did with orbital
notation, let's learn this notation by looking at some examples.
Example 1: Write the electronic configuration notation for an atom of carbon.
Begin solving this example problem by filling your board to represent the electrons found in an atom of carbon. Recall
that the symbol for carbon is C and the atomic number for carbon is six. Check the diagram below to see that you
properly filled your board. Remember that you can also check your work by counting the number
of discs which, in the case of carbon, should equal six.
As stated with orbital notation, begin writing the electron
configuration notation by writing down the element symbol
followed by a colon:
C:
Refer to your board and note the first orbit filled
outside the nucleus is the 1s orbit. Write down the 1s notation
following the colon and, instead of writing arrows to designate
electrons, write a superscript representing the number of
electrons found in the 1s orbit (in this case, 2).
C: 1s2
Nucleus
6
C
Carbon
12.0115
1s
2s
2p
x
y
x
y
z
3s
3p
4s
z
Continue the notation by referring again to your Board. Note that the next filled orbit is the 2s orbit. Write that
notation and include the superscript indicating the number of electrons found in the 2s orbit (2).
C: 1s2 2s2
Complete the notation by writing the next orbit which is the 2p orbits. Unlike the orbital notation, we will not
designate the specific locations of the x, y and z orbits. Instead, count the total number of electrons in the 2p orbits and
write that number (2 in our example of carbon) as a superscript following the 2p notation.
C: 1s2 2s2 2p2
To check your work, simply add up the superscripts. The total should equal the total number of electrons found in an
atom of that element. In our example (2+2+2=6), the sum of the superscripts is six which equals the total number of
electrons found in an atom of carbon (6).
Example 2: Write the electronic configuration notation for the electrons found in an atom of magnesium.
Begin your work by filling your Board with the
appropriate number of discs. Refer to your periodic
table of elements to find the element magnesium.
Note that the atomic number for magnesium is 12
(meaning that an atom of magnesium will have
12 electrons in its electron cloud). See the diagram to
make sure you've correctly filled your board.
Begin writing the electronic configuration notation for
magnesium by writing the symbol for magnesium followed
by a colon.
Mg:
Nucleus
12
Mg
1s
Magnesium
2s
24.31
2p
x
y
x
y
z
3s
3p
4s
z
Refer to your Board to continue writing the notation. Write down the first orbit filled and, as a superscript, the
number of electrons found in that orbit.
Mg: 1s2
Continue with the next orbit moving away from the nucleus.
Mg: 1s2 2s2
Continue writing the notation by referring again to your Board. As we stated in the first example, we will not
designate the specific locations of the three 2p orbits. Instead, we will count the total number of electrons in the 2p
orbits and write that total as a superscript following the 2p notation.
Mg: 1s2 2s2 2p6
To complete the electron configuration notation for magnesium, refer once again to your Board. Note that two discs
(electrons) remain in the 3s orbit. Write down the 3s notation followed by the superscript of 2 to represent those two
remaining electrons.
Mg: 1s2 2s2 2p6 3s2
Check your work by adding up the superscripts (2+2+6+2=12). The total equals 12 which equals the atomic number
(and number of electrons in an atom of magnesium). Like you did with orbital notation, you can still "read" the notation
telling the location of all electrons in an atom of magnesium. Let's try one more example of an element we have not yet
worked with.
Example 3: Write the electronic configuration notation for the electrons found in an atom of argon.
As in the two previous examples, first fill your Board with the appropriate number of discs to represent the electrons
found in an atom of argon. Find argon on your periodic table of elements. Argon, whose symbol is Ar, can be found on
the far right side of the table in the third series, or row, down. The atomic number for argon is 18 which means that you
should use 18 discs (9 of each color) to fill your Board. Refer to diagram below to check your work.
Begin writing the electron configuration notation
for argon by referring to your Board. Write down the
symbol for argon followed by a colon.
Nucleus
1s
Ar:
2s
Continue the notation by writing the notation for the
filled orbits as you move outward from the nucleus of the atom.
The next two orbits you encounter are the Is and 2s orbits.
2p
Ar: 1s2 2s2
x
y
x
y
z
3s
3p
4s
z
Continue with the next two orbits you encounter.
Ar: 1s2 2s2 2p6 3s2
Complete the notation by writing in the final orbit which contains electrons.
Ar: 1s2 2s2 2p6 3s2 3p6
Remember to check your work by adding up the superscripts. In this example 2+2+6+2+6=18 which equals the
number of electrons in an atom of argon. Like the two other ECN's (electronic configuration notations) we've completed,
you can "read" the notation and tell the locations of all electrons in an atom of argon.
Questions:
1. Write the ECNs for the following elements
a. carbon
b. beryllium
c. oxygen
d. neon
e. nitrogen
f. sodium
g. boron