Ch. 4 - Electrons in Atoms
IV. Electron
Configuration
(p. 105 - 116,
128 - 139)
C. Johannesson
Diagonal Rule
The diagonal rule is a memory device that
helps you remember the order of the filling
of the orbitals from lowest energy to
highest energy
Aufbau principle states that electrons fill
from the lowest possible energy to the
highest energy
Diagonal Rule
1
2
s
s
4 s
5 s
7
Steps:
1.
Write the energy levels top to bottom.
2.
Write the orbitals in s, p, d, f order. Write
2p
the same number of orbitals as the energy
level.
3 s
6

3p
4p
3d
3.
4d
4.
Draw diagonal lines from the top right to the
bottom left.
4f
To get the correct order,
By this point, we are
follow the arrows!
past the current periodic
5p
5d
5f
5g?
table so we can stop.
s
6p
6d
6f
6g?
6h?
s
7p
7d
7f
7g?
7h?
7i?
Why are d and f orbitals
always in lower energy
levels?
d and f orbitals require LARGE amounts of
energy
It’s better (lower in energy) to skip a sublevel
that requires a large amount of energy (d and f
orbitals) for one in a higher level but lower
energy
This is the reason for the diagonal rule! BE SURE
TO FOLLOW THE ARROWS IN ORDER!
C. Johannesson
A. General Rules
Pauli Exclusion Principle
Each orbital can hold TWO electrons
with opposite spins.
C. Johannesson
A. General Rules
Aufbau Principle
Electrons fill the
lowest energy
orbitals first.
“Lazy Tenant
Rule”
C. Johannesson
A. General Rules
Hund’s Rule
Within a sublevel, place one e- per
orbital before pairing them.
“Empty Bus Seat Rule”
WRONG
C. Johannesson
RIGHT
B. Notation
Orbital Diagram
O
8e-
1s
2s
Electron Configuration
2
2
4
1s 2s 2p
C. Johannesson
2p
Draw these orbital diagrams!
Carbon(C)
Nitrogen (N)
B. Notation
Longhand Configuration
S 16e- 1s2 2s2 2p6 3s2 3p4
Core Electrons
Valence Electrons
Shorthand Configuration
S
16e
2
4
[Ne] 3s 3p
C. Johannesson
C. Periodic Patterns
s
p
1
2
3
4
5
6
7
f (n-2)
d (n-1)
6
7
© 1998 by Harcourt Brace & Company
C. Johannesson
C. Periodic Patterns
Period #
energy level (subtract for d & f)
A/B Group #
total # of valence eColumn within sublevel block
# of e- in sublevel
C. Johannesson
C. Periodic Patterns
Example - Hydrogen
1
2
3
4
5
6
7
1st column
of s-block
1
1s
1st Period
s-block
C. Johannesson
Let’s Try It!
Write the electron configuration for the
following elements:
H
Li
N
Ne
K
Zn
Pb
Let’s Try It!
Write the electron configuration for the
following elements:
H
1s1
Li 1s2 2s1
N
1s2 2s2 2p3
Ne
1s2 2s2 2p6
K
1s2 2s2 2p6 3s2 3p6 4s1
Zn1s2 2s2 2p6 3s2 3p6 4s2 3d10
Pb1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10
5p6 6s2 4f14 5d10 6p2
C. Periodic Patterns
Shorthand Configuration
Core e-: Go up one row and over to the
Noble Gas.
Valence e-: On the next row, fill in the
# of e- in each sublevel.
1
2
3
4
5
6
7
C. Johannesson
C. Periodic Patterns
Example - Germanium
1
2
3
4
5
6
7
[Ar]
2
4s
10
3d
C. Johannesson
2
4p
D. Stability
Full energy level
Full sublevel (s, p, d, f)
Half-full sublevel
1
2
3
4
5
6
7
C. Johannesson
D. Stability
Electron Configuration Exceptions
Copper
EXPECT:
[Ar] 4s2 3d9
ACTUALLY:
[Ar] 4s1 3d10
Copper gains stability with a full
d-sublevel.
C. Johannesson
D. Stability
Electron Configuration Exceptions
Chromium
EXPECT:
[Ar] 4s2 3d4
ACTUALLY:
[Ar] 4s1 3d5
Chromium gains stability with a half-full
d-sublevel.
C. Johannesson
C. Johannesson
Try These!
Write the shorthand notation for:
Cu
W
[Ar] 4s1 3d10
Au
[Xe] 6s1 4f14 5d5
[Xe] 6s1 4f14 5d10
D. Stability
Ion Formation
Atoms gain or lose electrons to become
more stable.
Isoelectronic with the Noble Gases.
1
2
3
4
5
6
7
C. Johannesson
D. Stability
Ion Electron Configuration
Write the e- config for the closest Noble
Gas
EX: Oxygen ion  O2-  Ne
2O
10e
[He]
C. Johannesson
2
2s
6
2p
Keep an Eye On Those Ions!
Electrons are lost or gained like they
always are with ions… negative ions have
gained electrons, positive ions have lost
electrons
The electrons that are lost or gained
should be added/removed from the
outermost energy level (not the highest
orbital in energy!)
Keep an Eye On Those Ions!
Tin
Atom: [Kr] 5s2 4d10 5p2
Sn+4 ion: [Kr] 4d10
Sn+2 ion: [Kr] 5s2 4d10
Note that the electrons came out of the
outermost energy level, not the highest
energy orbital!
Keep an Eye On Those Ions!
Bromine
Atom: [Ar] 4s2 3d10 4p5
Br- ion: [Ar] 4s2 3d10 4p6
Note that the electrons went into the
outermost energy level, not the highest
energy orbital!
Try Some Ions!
Write the longhand notation for these:
2 2s2 2p6
1s
F
2
+
1s
Li
2 2s2 2p6  note this is the
+2
1s
Mg
same as F- this is called
isoelectronic
Write the shorthand notation for these:
Br[Ar]4s2 3d10 4p6
+2
Ba
[Kr]5s2
4d10
5p6
Al+3
[He]2s2 2p6