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C. Johannesson
IV. Electron Configuration(p. 105 - 116,
128 - 139)
Ch. 4 - Electrons in Atoms
Pauli Exclusion Principle
1. Principal # 2. Azim(Ang. Mom.) # 3. Magnetic # 4. Spin #
energy level
sublevel (s,p,d,f)
orbital
electron
No two electrons in an atom can have the same 4 quantum numbers.
Each e- has a unique “address.”
A. General Rules
Pauli Exclusion Principle
Each orbital can hold TWO electrons
with opposite spins.
Spin is the only difference between
these two electrons’ quantum states.
O 8e-
Orbital Diagram: shows all the electrons in an atom as arrows. Each box is an orbital. Joined orbitals are sublevels.
B. Notation
1s 2s 2p UP arrows have a ms of +1/2
DOWN arrows have a ms of -1/2
C. Johannesson
A. General Rules
Aufbau Principle
Electrons fill the lowest energy orbitals first.
“Lazy Tenant Rule”
RIGHTWRONG
A. General Rules
Hund’s Rule
Within a sublevel, place one e- per orbital (spin-parallel) before pairing them.
“Empty Bus Seat Rule”
1s1Just one electron in the 1s sublevel.
1
2
3
4 5
6
7
C. Electron Configuration
Gives the energy state for ALL the electrons in an atom.
Hydrogen’s configuration is simplest and shortest because H only contains one electron.
1s2
C. Electron Configuration
Gives the energy state for ALL the electrons in an atom.
Lithium contains 3 electrons: 2 in the 1s
(#1 & #2) 1 in the 2s
(#3) 2s1
1 23
1s2Sulfur’s last 4 electrons are in 3p.
C. Electron Configuration
Gives the energy state for all the electrons in an atom.
Sulfur’s configuration needs to include ALL 16 of its electrons.
1 23 4 5 6 7 8 9 10
11 12 13 14 15 16
2s22p63s23p4
All e-configs start at 1s.Powers should add up to atomic #
(2+2+6+2+4=16)
C. Johannesson
O 8e-
Orbital Diagram
Electron Configuration
1s2 2s2 2p4
B. Notation
1s 2s 2p
C. Johannesson
Shorthand (Noble Gas) Configuration
S 16e-
Valence ElectronsCore Electrons(up to previous Noble)
S 16e- [Ne-10] 3s2 3p4
1s2 2s2 2p6 3s2 3p4
B. Notation
Longhand Configuration
C. Johannesson
1
2
3
4
5
6
7
C. Periodic Patterns
Aufbau Principle: electrons always fill in order from lowest energy to highest energy.
Atomic numbers on the periodic table count electrons in the order they fill, so the order is always the same.
Don’t forget where the f-block goes!
C. Periodic Patterns
Aufbau Series: the order in which electrons fill energy levels & sublevels.
3p64s21s2 2p63s2 4p63d102s2
…5p6 6d10
4d10...4f146s2 5d10
5s2
7p66p6 7s2 5f14
C. Periodic Patterns
Orbital diagrams show the same information as electron configuration in a different way.
The Aufbau Series still applies!
1s2
C. Electron Configuration
Example – Nickel (Ni #28)
Ni
1 2
2s22p63s23p64s23d8
3 4 5 6 7 8 91011 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28
2+2+6+2+6+2+8 = 28
C. Johannesson
1
2
3
4
5
6
7
C. Periodic Patterns
Shorthand Configuration Core e-: Start with the noble gas from
the previous period. Valence e-: On the next row, fill in the #
of e- in each sublevel.
C. Johannesson
[Ar-18]
1
2
3
4 5
6
7
4s2 3d10 4p2
C. Periodic Patterns
Example - Germanium
C. Johannesson
C. Periodic Patterns
Period # energy level (remember d & f don’t line
up with s & p!)A/B Group #
total # of valence e-
Column within sublevel block # of e- in sublevel
C. Johannesson© 1998 by Harcourt Brace & Company
s p
d (n-1)
f (n-2)
1234567
67
C. Periodic Patterns
C. Johannessons-block1st Period
Hydrogen: 1s11st column of s-block
1
2
3
4 5
6
7
C. Periodic Patterns
Elements in the same column have similar valence configurations.
s-block5th Period
[Kr-36]5s11st column of s-block
1
2
3
4 5
6
7
C. Periodic Patterns
Rubidium (Rb #37)
C. Johannesson
Full energy level
1
2
3
4 5
6
7
Full sublevel (s, p, d, f)Half-full sublevel
D. Stability
C. Johannesson
Electron Configuration Exceptions
Copper
EXPECT: [Ar] 4s2 3d9
ACTUALLY: [Ar] 4s1 3d10
Copper gains stability with a full d-sublevel.
D. Stability
C. Johannesson
Electron Configuration Exceptions
Chromium
EXPECT: [Ar] 4s2 3d4
ACTUALLY: [Ar] 4s1 3d5
Chromium gains stability with a half-full d-sublevel.
D. Stability
C. Johannesson
1
2
3
4 5
6
7
D. Stability
Ion Formation Atoms gain or lose electrons to become
more stable. Isoelectronic with the Noble Gases.
C. Johannesson
O2- 10e- [He] 2s2 2p6
D. Stability
Ion Electron Configuration
Write the e- config for the closest Noble Gas
EX: Oxygen ion O2- Ne
