Orbital Diagrams,
Electron Configurations,
&
Valence Electrons
Bohr’s Model: electrons would exist in
different rings around the nucleus just like
the planets are in different orbits around
the sun. This is sometimes called the
planetary model of the atom
Bohr’s Atom
7 orbits correspond to 7 periods
on Periodic Table.
Which Orbit has the
lowest energy?
n = 1, the orbit closest to the
nucleus.
Bohr’s model was replaced by
the quantum mechanical
model of the atom.
• This new model uses principle
quantum levels that are similar
to Bohr’s orbits, but are then
divided into sublevels
The principle quantum level is
a number from 1-7, with 1
being the lowest energy
and 7 being the highest in
energy.
The sublevels are s, p, d, and f
These numbers and letters correspond to the
periods and the “blocks” on the periodic
table.
• Each sublevel has a least one
orbital.
• Each orbital can hold 2 electrons
The s sublevel only has 1 orbital, and
each orbital holds 2 electrons
Which matches the
2 elements in each
period of the s block
Shape: Sphere
The p sublevel has 3 orbitals, and each
orbital holds 2 electrons, for a total of 6
electrons – Matching the 6 elements in
each period of the p block
Shape:
dumbbell or
peanut
The d sublevel has 5 orbitals, and each
orbital holds 2 electrons, for a total of 10
electrons – matching the 10 elements in
each period of the d block
Shape: clover/
double dumbbell
The f sublevel has 7 orbitals, and each
orbital holds 2 electrons, for a total of 14
electrons – matching the 14 elements
Funky /
flower
We put together the principle
quantum number and sublevel letter
to talk about a specific orbital
But not all sublevels are possible for
each energy level.
Principle Quantum Level
1
2
3
4–7
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
Possible Sublevels
s
s, p
s, p, d
s, p, d, f
5s 5p 5d 5f
6s 6p 6d (6f)
7s 7p (7d 7f)
The arrangement of electrons
in an atom is called an orbital
diagram or electron
configuration.
1) There are three rules that
we must follow when making
an orbital diagram (OD) or an
electron configuration (EC):
A) The aufbau principle says
electrons must fill lower energy
levels before electrons can fill
higher energy levels.
This means 1s is filled before 2s,
etc
B) The Pauli exclusion principle
says that only two electrons can
fill each orbital…and they must
have opposite spins.
No
Yes
C) Hund’s rule says electrons must
spread out in the orbitals of each
sublevel (p, d, or f) before they double
up.
Yes
No
□□□
□□□
2p
2p
2) If we use boxes to represent
orbitals, then the following aufbau
diagram shows all the possible places
an electron could be:
Remember:
s
p
d
f
has 1 orbital…..holds 2 electrons
has 3
…..holds 6 electrons
has 5
…..holds 10 electrons
has 7
…..holds 14 electrons
Notice that the energy increases from
bottom to top,
High
Energy
Low
Energy
and some of the orbitals do not fill in
the same number order as the others.
Fill from the bottom to the top,
spreading out the electrons before
doubling them up
Hydrogen
H
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Helium
He
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Completely
Filled
Lithium
Li
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Beryllium
Be
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Boron
B
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Carbon
C
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Nitrogen
N
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Oxygen
O
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Fluorine
F
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Neon
Ne
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Completely
Filled
Sodium
Na
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Magnesium
Mg
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Aluminum
Al
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Silicon
Si
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Phosphorus
P
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Sulfur
S
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Chlorine
Cl
□ □ □ 3p
□ 3s
□ □ □ 2p
□ 2s
□ 1s
Argon
Ar
□ □ □ 3p
□ 3s
□
□ 2s
□ 1s
Completely
Filled
□ □ 2p
3) The correct order of filling is: 1s 2s 2p 3s 3p
4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
Notice: s block fills in period 1
p block fills in period 2
d block fills in period 3: which is 1 behind the actual period
f block fills in period 4: which is 2 behind the actual period
n = period #
s & p block fill at n
d block fills at n – 1
f block fills at n - 2
4) Orbital Diagram:
Orbitals are
sometimes shown as boxes in a
horizontal row
Remember: s = 1 orbital
p = 3 orbitals
d = 5 orbitals
f = 7 orbitals
5) Arrows are used to represent
the electrons, so if two arrows go
in the same box, one points up
and the other points down.
Nitrogen
N
7 electrons
□ □ □ 2p
□ 2s
□ 1s
Becomes:
□
□
□□□
1s
2s
2p
Cobalt (27 electrons – 27 arrows)
□ □ □□□ □ □□□ □ □□□□□
1s 2s
2p 3s
3p 4s
3d
Cations and anions
• * Ions: work the same way but remember that
electrons are negative. +2 means you lost two
electrons, -2 means you gained two electrons.
Try Bromine
Bromine (35 electrons)
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s
2p 3s
3p 4s
3d
4p
Try Oxygen, O2- and Gallium on
the back of your notes
Oxygen
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s
2p 3s 3p
4s
3d
4p
-2
O
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s
2p 3s 3p
4s
3d
4p
Gallium
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s
2p 3s 3p
4s
3d
4p
6) Electron Configuration: Instead of
drawing boxes and arrows, the
number of electrons in each sublevel
is turned into a superscript and is
written with the quantum number and
the sublevel letter.
A) If all the orbitals are filled, the
entire sequence would be:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
2
10
6
2
14
10
6
5s 4d 5p 6s 4f 5d 6p
7s2 5f14 6d10 7p6
Nitrogen
N
□
□
□□□
1s
2s
2p
Becomes:
1s2 2s2 2p3
Cobalt
□ □ □□□ □ □□□ □ □□□□□
1s 2s
2p 3s
3p 4s
Becomes:
1s2 2s2 2p6 3s2 3p6 4s2 3d7
3d
Try Bromine, Oxygen, O2-, Ca 2+
and Gallium on the back of your
notes
Bromine (35 electrons)
□ □ □□□ □ □□□ □ □□□□□ □□□
1s 2s
2p 3s
3p 4s
3d
Becomes:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
4p
Electron configurations for:
Oxygen:
2
2
4
1s 2s 2p
O2- : 1s22s22p6
2+
Ca
:
2
2
6
2
6
1s 2s 2p 3s 3p
Gallium:
2
2
6
2
6
2
10
1
1s 2s 2p 3s 3p 4s 3d 4p
7) Short cut: Noble gas
configuration. Instead of writing
out the entire electron configuration,
we can use the previous noble gas to
take the place of part of the electron
configuration: must start with a noble
gas
Example:
2
2
6
2
1s 2s 2p 3s
Magnesium:
Neon: 1s22s22p6
Noble Gas configuration:
Magnesium: [Ne] 3s2
Example:
Polonium:
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p4
Xenon:
1s22s22p63s23p64s23d104p65s24d105p6
Polonium:[Xe]
2
14
10
4
6s 4f 5d 6p
Try Bromine, Oxygen, O2-, Ca 2+
and Gallium on the back of your
notes
Noble gas configurations
Bromine [Ar] 4s2 3d10 4p5
Oxygen: [He] 2s22p4
O2-: [He] 2s22p6
Ca2+ : [Ne] 3s23p6
Gallium: [Ar] 4s23d104p1
8) Valence Electrons: Electrons in the
outer-most orbital – which is the
highest energy level.
Very important: electrons involved in
chemical bonds – determine chemical
properties of element
These electrons are called
valence electrons.
Only the s and p block electrons are
counted…so the number of valence
electrons must be a number from 1 to 8
9) Electron Dot Diagrams (Lewis Dot
Diagrams):
The number of valence electrons makes
a big difference in how the element
will bond, so to make it easy to
predict, we draw electron dot
diagrams.
A) In an electron dot diagram, we use
the symbol of the element and dots to
represent the number of valence
electrons. The number of dots
matches the group number on the
Periodic Table.
B) Only s and p electrons with the
highest quantum number count for
dot diagrams, even if there are d and
f electrons
Lithium =
So
2
1
1s 2s
Li
Beryllium =
So
2
2
1s 2s
Be
Boron =
So
2
2
1
1s 2s 2p
B
Carbon = [He]
So
2
2
2s 2p
C
Nitrogen = [He]
So
N
2
3
2s 2p
Oxygen =
So
2
2
4
1s 2s 2p
O
Fluorine =
So
2
2
5
1s 2s 2p
F
Neon =
So
2
2
6
1s 2s 2p or
[Ne]
Ne
All noble gases have full outer shells:
8 valence electrons (except He which is
full at 2, since it only has the s orbital)
Magnesium = 1s22s22p63s2
So
Magnesium = 1s22s22p63s2
So
Mg
Mg
Polonium:
1s22s22p63s23p64s23d104p65s24d105p66s2
4f145d106p4
Polonium:
1s22s22p63s23p64s23d104p65s24d105p66s2
4f145d106p4
So
Po
Po
Look
at
your
Periodic
Table
Notice:
Look at your Periodic Table Notice: the A
The
A number
group number
= theofnumber
group
= the number
valence of
valence
electronselectrons (except for He)
1A
8A
2A
3A 4A 5A 6A 7A