Electron Configurations
Unit 3.7 and 3.8
Orbitals
• Region outside the nucleus where
the electron has the highest
probability of being.
• Drawn with a fuzzy border like the
atmosphere around earth.
• No defined border because there is
a small chance the electron may be
outside this region.
• The orbital pictured to the right is
the 1s orbital. It is the lowest
energy level for hydrogen.
Principal Energy Levels
• Remember Bohr
4 Sublevels
demonstrated that
hydrogen had 4 main 3 Sublevels
energy levels.
• These energy levels are 2 Sublevels
called principal energy
levels.
1 Sublevel
• Each principal energy
level can be divided into
sublevels.
Energy Level 4
Energy Level 3
Energy Level 2
Energy Level 1
Principal Energy Levels
• The first energy level has one
sub energy level.
• This sub energy level is
known as the 1s orbital.
• The 1 stands for the principal
energy level and the s stands
for its shape (spherical)
• The 1s orbital can hold 2
electrons.
• Remember the first floor of
the “Hog Hilton” had one
room that could hold two
pigs.
Energy Level 4
Energy Level 3
Energy Level 2
Energy Level 1
2 electrons in
the 1st principal
energy level.
Principal Energy Level 2
• The second energy level has 2
sub energy levels. 2s and 2p
• The 2s orbital is just like the
1s orbital but larger in size.
• The 2p sublevel consists of 3
orbitals.
• Each of the 2p orbitals holds
two electrons for a total of 6.
Energy Level 4
Energy Level 3
Energy Level 1
2px 2py 2pz
8 electrons in the
2nd principal
energy level.
2p Orbitals
• The three 2p
orbitals are
“lobed”
shaped.
• The x, y, and z
tell which axis
the lobes are
parallel to.
Principal Energy Level 3
• The 3rd energy level has
three sublevels: 3s, 3p and
3d.
• The 3s orbital is shaped
like the 1s and 2s; it is just
larger and further from the
nucleus.
• The 3 p sublevel also has 3
orbitals. (3px, 3py, and 3pz)
They are shaped like the 2p
orbitals only larger.
• The 3d sublevel has 5
orbitals. Each orbital can
hold 2 electrons for a total
of 10 electrons
Energy Level 4
Energy Level 1
3s
3px 3py 3pz
3d orbitals
3rd energy level
2nd energy level
1st energy level
18 electrons in
the 3rd principal
energy level.
There are 5 3d orbitals
You don’t need
to know these
shapes.
Principal Energy Level 4
• The 4th energy level has
four sublevels: 4s, 4p, 4d
and 4f.
• There is one 4s orbital,
three 4p orbitals, five 4d
orbitals just like the 3s,
3p and 3d orbitals
except they are larger.
• The 4f sublevel has 7
orbitals. Each orbital can
hold 2 electrons for a
total of 14 electrons
Energy Level 3
Energy Level 2
Energy Level 1
4s
4px 4py 4pz
Five 4d orbitals
Seven 4f orbitals
Energy Level 3
32 electrons in
the 4th principal
energy level.
Energy Level 2
Energy Level 1
There are seven 4f orbitals
You don’t need
to know these
shapes.
Electron Arrangements
• The most attractive orbital to an electron in an
atom is always the 1s, because this orbital is
closest to the nucleus.
• Hydrogen has 1 electron in this orbital so its
electron configuration is: 1s1
• Helium has 2 electrons in this orbital so its
electron configuration is: 1s2
• Elements with more than two electrons fill the 1s
orbital first before filling higher energy orbitals.
Electron Arrangements Continued…
• The 1s orbital gets filled first, then the 2s, then
the 2p, then the 3s followed by the 3p.
• Since lithium has 3 electrons, two can fit in the
1s orbital and the last goes in the 2s orbital.
• Therefore the electron configuration for lithium
is:
Time for Electron Configuration
Practice!
Take a Shortcut…
• Electron Configuration for Sulfur & Neon
• S (16 electrons):
1s22s22p63s23p4
• Ne (10 electrons): 1s22s22p6
• Instead of writing out the full electron
configuration for sulfur use the NOBLE GAS
notation:
[Ne] 3s2 3p4
Noble Gas Notation Practice:
• Write the regular electron configuration for
boron and helium:
• B (5 electrons):
1s22s22p1
• He (2 electrons):
1s2
• Now write the noble gas notation for Boron:
[He] 2s22p1
Orbital Diagrams
• Orbital diagrams show all of the
electrons in an atom.
• They are similar to the Hog Hilton
drawings you made.
• Just like the hogs in the Hog Hilton
two electrons can fit in each orbital
but they must be spinning in opposite
directions.
• We represent this on an orbital
diagram as an up and a down arrow.
1s
Orbital Diagrams
• Electrons spread out as far as possible before
pairing (because of repulsion).
• This is known as Hund’s Rule or the “Empty
Bus Seat Rule”
• If there are 4 electrons in the p-orbital:
WRONG
RIGHT
Time for Orbital Diagram Practice!
Orbital Filling order
• What is the electron configuration for
Potassium?
• It is actually:
1s22s22p63s23p64s1
• We fill up the 4s orbital before filling up
the 3d orbitals.
• Why?
▫ Because the d and f orbitals require a lot of
energy to fill.
This make sense…
• Remember the periodic table you
colored with the s, p, d and f
blocks?
• We could’ve used it to guess what
the last orbital for potassium would
be based on its location in the
periodic table.
• It is in the s-block.
• It is in the first column of the block
• It is in the fourth period.
• So it should end with:
1
4s
Orbital Filling Order
• The diagram to the
right shows the
order in which the
orbitals get filled.
• Notice that the
fourth energy level
starts to get filled
before the third
energy level is
completely filled.
• Etc.
Valance Electrons
• The definition hasn’t changed!
• Still the number of electrons in the highest
energy level.
• Example: Potassium-1s22s22p63s23p64s1
Core Electrons Valance Electron
Practice Problem
• Write the electron configuration for Gallium &
identify the VALENCE electrons!
• Gallium (31 Electrons):
•1s22s22p63s23p64s23d104p1
Core Electrons Valance Electrons
•Gallium has 3 total valance electrons!
•This makes sense because it is in group
3A!
Periodic Table Patterns Review
s
1
2
3
4
5
6
7
p
d (n-1)
f (n-2)
Periodic Patterns Continued
• The “A” column numbers= number of total
valance electrons.
• The period number= energy level (subtract for d
and f)
• Column number within a block = number of
electrons in that orbital.
Example: Strontium
11
22
33
44
55
66
77
Previous
Noble Gas
2
[Kr]5s
Period 5
S Block
Second column
in the block
Practice Problem
• Use the patterns on the table to figure out the
electron configuration for Germanium.
11
22
33
44
55
66
77
2
10
[Ar]4s 3d
2
4p
Time for Practice!