Orbital Diagrams
& Electron Configurations
for Atoms and Ions
Orbital diagrams represent the
arrangement of electrons in orbitals.
• boxes or lines represent each orbital
• arrows within boxes represent the electrons
• max two per box
• opposite direction (represents opposite spin)
Section 3.5
e.g., Hydrogen
(Z=1)
e.g., Helium
(Z=2)
1s
The aufbau principle:
• The atom is “built up” by
progressively adding
electrons.
• Electrons will fill the lowest
available energy levels first,
before filling higher levels.
1s
Within a principal energy level,
s<p<d<f
Example: 3s fills before 3p
But… the (n+1)s orbitals always
fill before the nd orbitals.
Example: 5s fills before 4d
Practice!
Orbital filling order for elements
beyond Period 2 …
...corresponds to atom’s
location in periodic table!
Draw an orbital diagram for beryllium (Z=4)
1s
Guidelines for drawing orbital diagrams
1s
1. Fill orbitals in order of increasing energy.
2s
2p
2. Orbitals of the same energy level must be filled before moving
onto the next energy level.
3. Place electrons singly into orbitals
within a sublevel before
Hund’s rule: To achieve the
any pairing occurs.
lowest possible energy, electrons
will spread out singly before
pairing up within an orbital.
1s
2s
7
N
nitrogen
14.01
2p
Ti
8
O
oxygen
16.00
Orbital diagrams for ions
• anion (negative charge): ADD appropriate number of electrons
• cation (positive): REMOVE appropriate number of electrons
Example:
Oxide ion, O2-
Before beginning, ask yourself:
a) How many
Draw orbital diagrams for:
a) Sulfur (Z=16)
1s
e-
Practice!
in an oxygen atom?
b) How many e- do I add/remove?
c) What’s the new total number of e-?
2s
2p
b) Iron (Z=26)
c) Aluminum (Z=13)
Tip:
Use lines instead of
boxes to represent
the orbitals.
An electron configuration is a
shorthand notation that provides the
same information as the orbital diagram.
Practice!
Draw orbital diagrams for:
b) Iron (Z=26)
d) Gold (Z=79)
B
boron
10.81
a) Sulfur (Z=16)
c) Aluminum (Z=13)
5
Tip:
Use lines instead of
boxes to represent
the orbitals.
Guidelines for writing electron configurations
Practice!
1. Write out subshells that have electrons in them.
2. Use superscripts to indicate how many electrons are in each subshell.
Write electron configurations for:
a) Sulfur (Z=16)
b) Iron (Z=26)
c) Aluminum (Z=13)
d) Gold (Z=79)
Electron configurations can be abbreviated:
Two exceptions to the pattern: Cr and Cu
Gold: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d9
Possible explanation:
Filled and half-filled sub-shells have lower
energy than unfilled ones  more stable
= [Xe] 6s2 4f14 5d9
Nearest preceding
noble gas
Practice!
Write abbreviated electron
configurations for the atoms
you just completed
Electron configurations can explain periodic properties.
Chromium:
[Ar]
4s
3d
Learning Checkpoint
You can use the position on the periodic table to write
out the electron configuration for an element.
Elements in a group:
• same valence electron configuration
• common properties: chemical, physical
Electron configurations of ions
Na: 1s2 2s2 2p6 3s1
Na+:
Mg:
1s2 2s2 2p6 3s2
1s2 2s2 2p6
Al:
1s2 2s2 2p6 3s2 3p1
1s2 2s2 2p6
Why do atoms
form ions?
All of these ions are
ISOELECTRONIC
with Neon.
Weird quirk:
Even though the s orbitals fill first, they lose first when forming ions
Zn:
Zn2+:
O:
1s2 2s2 2p4
1s2 2s2 2p6
•
•
•
•
3d10
“Transition Metals”
d-block elements
examples?
more orbitals = more possibilities
[Xe] 6s2 4f14 5d106p2
Lose 2e-
3d
Pb2+:
Summary
• Orbital diagrams use boxes
or lines to visually represent
the orbitals of atoms. Arrows
are used to represent
electrons.
1s2 2s2 2p6
MO ORBITALS
MO PROBLEMS
Pb:
…also
gives up
more easily
[Xe]
• Electron configurations
convey the same
information, but in a more
condensed form.
1s2 2s2 2p5
Multivalent metals can have more
than one ionic charge.
[Ar]
[Ar] 4s0 3d10
4s easier
to fill…
4s2
F:
F- :
6s2
4f14 5d106p0
Lose 4e-
Pb4+:
[Xe] 6s0 4f14 5d106p0