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Unit 3: Electrons!
Beginnings with Bohr – Page 6
• Atomic theory (Niels Bohr) involved
absorption and emission of light.
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Schrodinger – Page 9
• Mathematical equations are used to
describe wave properties of electrons.
• Based on probable location of electrons –
Heisenberg Uncertainty Principle.
Quantum Mechanics
• Orbital (“electron cloud”)
– Region in space where there is 90%
probability of finding an electron
90% probability of
finding the electron
Electron Probability vs. Distance
Electron Probability (%)
40
30
20
10
0
0
50
100
150
200
250
Distance from the Nucleus (pm)
Orbital
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Orbitals
• The location of an electron is described
with 4 terms.
- Energy Level
- Sublevel
- Orbital
- Spin
Sublevels
• There are four sublevel.
-s
-p
-d
-f
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Energy Level
• Describes the energy and distance from the
nucleus.
• Whole numbers, ranging from 1 to 7.
Orbital Shapes – s sublevel
- s for “sphere”
- The s sublevel contains only 1 orbital.
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P Sublevel
• 3 orbitals present in this sublevel.
• P for “petal/peanut”
D Sublevel
• 5 orbitals present in this sublevel.
• D for “double peanut/petal”
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F Sublevel
• 7 orbitals present in this sublevel.
• F for “flower”
Summary
Energy
Level
Sublevels
Present
# of
Orbitals
Total # of
electrons
in Energy
Level
1
2
3
4
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Arrangement of E- (Page 10)
• Electrons are arranged according to a few
rules.
– Aufbau Principle
– Pauli’s Exclusion Principle
– Hund’s Rule
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Aufbau Principle – Page 9
• As protons are added one by one to
the nucleus to build up the elements,
electrons are similarly added to
orbitals
• Electrons fill in low energy orbitals
before high energy orbitals
Increasing energy
Aufbau Principle – Page 10
7s
6s
5s
7p
6p
6d
5p
4d
4p
4s
3p
3s
2p
2s
5d
5f
4f
3d
He with 2
electrons
* orbital energy order found
on periodic table
1s
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Pauli’s Exclusion – Page 9
• No 2 electrons in the same atom can have
the same 4 quantum numbers.
• Each orbital can only hold 2 electrons and
they will have opposite spins.
– Example
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Hund’s Rule – Page 9
• When there are multiple orbitals, one
electron goes in each before pairing takes
place.
Orbital Notation – Page 13
• Orbital Notation shows the energy level,
sublevel, orbital, and spin for every
electron in an atom.
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Practice
• Step 1: Start by drawing out the orbitals in
the correct order.
• Step 2: Determine the total number of
electrons.
Practice
• Step 3: Start arranging the electrons
• Step 4: Follow the rules!
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Quantum Numbers
• Four Quantum Numbers:
– Specify the “address” of each electron
in an atom
UPPER LEVEL
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Quantum Numbers
Principal Quantum Number ( n )
Angular Momentum Quantum # ( l )
Magnetic Quantum Number ( ml )
Spin Quantum Number ( ms )
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Quantum Numbers
1. Principal Quantum Number ( n )
– Energy level
1s
– Size of the orbital
2s
– n2 = # of orbitals in
the energy level
=1-7
3s
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Quantum Numbers
2. Angular Momentum Quantum # ( l )
– Energy sublevel
– Shape of the orbital
s
p
d
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f
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The angular momentum quantum
number
Allowed values of l depend on the value of n and can
range from 0 to n – 1
Copyright © 2006 Pearson Benjamin Cummings. All rights reserved.
Quantum Numbers
3. Magnetic Quantum Number ( ml )
– Orientation of orbital
– Specifies the exact orbital within each sublevel
– ml can range from –l to l in integral steps
–
ml = l, -l + l, . . . 0 . . ., l – 1, l
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Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 336
Quantum Numbers
4. Spin Quantum Number ( ms )
– Electron spin  +½ or -½
– An orbital can hold 2 electrons that spin in
opposite directions.
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Quantum Numbers
n
shell
1, 2, 3, 4, ...
l
subshell
0, 1, 2, ... n - 1
ml
orbital
- l ... 0 ... +l
ms
electron spin
+1/2 and - 1/2
Let’s try quantum #’s!
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Allowed Sets of Quantum Numbers for Electrons in Atoms
Level n
1
l
0
0
Sublevel
Orbital ml
Spin ms
2
0
0
1
3
1
0
-1
0
0
1
1
0
-1
2
1
2
0
-1
-2
= +1/2
= -1/2
Electron Orbitals:
Electron
orbitals
Equivalent
Electron
shells
(a) 1s orbital
(b) 2s and 2p orbitals
c) Neon Ne-10: 1s, 2s and 2p
1999, Addison, Wesley, Longman, Inc.
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What sort of covalent bonds
are seen here?
H
H
H
O
O
O
H
O
(b) O2
(a) H2
H
H
O
H
O
H
H
O
H
H
H
C
H
H
H
H
(c) H2O
(d) CH4
THIS SLIDE IS ANIMATED
IN FILLING ORDER 2.PPT
H = 1s1
1s
He = 1s2
1s
Li = 1s2 2s1
1s
2s
1s
2s
1s
2s
2px 2py 2pz
1s
2s
2px 2py 2pz
Be = 1s2 2s2
C = 1s2 2s2 2p2
S = 1s2 2s2 2p63s2 3p4
3s
3px 3py 3pz
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26 electrons.
Iron has ___
Fe = 1s1 2s22p63s23p64s23d6
1s
2px 2py 2pz
2s
3px 3py 3pz
3s
4s
6s
6p
5d
5s
5p
4d
4p
3d
3d
3d
3d
3d
3d
4f
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e-
eee-
e-
+26
e-
e-
e-
ee-
e-
ee-
e-
e-
4s
e-
ee-
ee-
18
e-
e-
e-
e-
18
Arbitrary
Energy Scale
3s
3p
8
ee-
2s
2p
8
1s
2
NUCLEUS
Electron Configurations
Orbital Filling
Element
1s
2s
2px 2py 2pz
3s
Electron
Configuration
H
1s1
He
1s2
C
NOT CORRECT
1s22s1
Violates Hund’s
Rule
1s22s22p2
N
1s22s22p3
O
1s22s22p4
F
1s22s22p5
Ne
1s22s22p6
Na
1s22s22p63s1
Li
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Electron Configurations
Orbital Filling
Element
1s
2s
2px 2py 2pz
3s
Electron
Configuration
H
1s1
He
1s2
Li
1s22s1
C
1s22s22p2
N
1s22s22p3
O
1s22s22p4
F
1s22s22p5
Ne
1s22s22p6
Na
1s22s22p63s1
Filling Rules for Electron Orbitals
Aufbau Principle: Electrons are added one at a time to the lowest
energy orbitals available until all the electrons of the atom
have been accounted for.
Pauli Exclusion Principle: An orbital can hold a maximum of two electrons.
To occupy the same orbital, two electrons must spin in opposite
directions.
Hund’s Rule: Electrons occupy equal-energy orbitals so that a maximum
number of unpaired electrons results.
*Aufbau is German for “building up”
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Filling Rules for Electron Orbitals
Aufbau Principle: Electrons are added one at a time to the lowest
energy orbitals available until all the electrons of the atom
6s
6p
5d
4f
have been accounted for.
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5s
5p
4d
18
Pauli Exclusion Principle: An orbital
can
hold
a maximum of two electrons.
4s
4p
3d
To occupy the same orbital, two electrons must spin in opposite
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directions. Arbitrary
North
South
3s
3p
Energy Scale
8
-
-
Hund’s Rule: Electrons occupy equal-energy orbitals so that a maximum
2s
2p
number of unpaired electrons results.
8
1s
*Aufbau is German for “building up”
S
2
N
NUCLEUS
Spin Quantum Number, ms
North
Electron aligned with
magnetic field,
South
N
S
Electron aligned against
magnetic field,
ms =its
-½
ms = +behaves
½
The electron
as if it were spinning about an axis through
center.
This electron spin generates a magnetic field, the direction of which depends
on the direction of the spin.
Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 208
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Energy Level Diagram of a Many-Electron Atom
6s
6p
5d
4f
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5s
5p
4d
18
4s
4p
3d
18
Arbitrary
Energy Scale
3s
3p
8
2s
2p
8
1s
2
NUCLEUS
O’Connor, Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles 1982, page 177
Maximum Number of Electrons
In Each Sublevel
Maximum Number of Electrons In Each Sublevel
Sublevel
Number of Orbitals
Maximum Number
of Electrons
s
1
2
p
3
6
d
5
10
f
7
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LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 146
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Quantum Numbers
n
shell
1, 2, 3, 4, ...
l
subshell
0, 1, 2, ... n - 1
ml
orbital
- l ... 0 ... +l
ms
electron spin
+1/2 and - 1/2
Order in which subshells are filled
with electrons
1s
2s
2p
3s
3p
3d
4s
4p
4d
4f
5s
5p
5d
5f
6s
6p
6d
7s
2
2
6
2
6
2
10
6
2
10
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d …
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Hydrogen
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
H = 1s1
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Helium
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
He = 1s2
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Lithium
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
Li = 1s22s1
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Carbon
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
C = 1s22s22p2
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Nitrogen
4f
Bohr Model
N
Hund’s Rule “maximum
number of unpaired
orbitals”.
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
N = 1s22s22p3
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Fluorine
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
F = 1s22s22p5
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Aluminum
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
Al = 1s22s22p63s23p1
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Argon
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
NUCLEUS
H He Li C N Al Ar F
Fe La
Ar = 1s22s22p63s23p6
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Iron
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
Fe = 1s22s22p63s23p64s23d6
NUCLEUS
H He Li C N Al Ar F
Fe La
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Arbitrary Energy Scale
Energy Level Diagram
6s
6p
5d
5s
5p
4d
4s
4p
3d
3s
3p
Lanthanum
4f
Bohr Model
N
2s
2p
1s
Electron Configuration
La = 1s22s22p63s23p64s23d10
NUCLEUS
H He Li C N Al Ar F
Fe La 4s23d104p65s24d105p66s25d1
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Shorthand Configuration
A neon's electron configuration (1s22s22p6)
B
third energy level
[Ne] 3s1
C
D
one electron in the s orbital
orbital shape
Na = [1s22s22p6] 3s1
electron configuration
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Shorthand Configuration
Element symbol
Electron configuration
Ca
[Ar] 4s2
V
[Ar] 4s2 3d3
F
[He] 2s2 2p5
Ag
[Kr] 5s2 4d9
I
[Kr] 5s2 4d10 5p5
Xe
[Kr] 5s2 4d10 5p6
22p64s
[He] 2s[Ar]
3s223d
3p664s23d6
Fe
[Rn] 7s2 5f14 6d4
Sg
General Rules
• Pauli Exclusion Principle
Wolfgang Pauli
– Each orbital can hold TWO electrons with
opposite spins.
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General Rules
6d
Aufbau Principle
7s
5d
– Electrons fill the
lowest energy
orbitals first.
6s
5f
6p
5d
6s
4d
5s
3d
3p
4f
5p
5s
4p
4s
6d
7s
4f
5p
4d
Energy
– “Lazy Tenant
Rule”
5f
6p
4p
3d
4s
3p
3s
3s
2p
2p
2s
2s
1s
1s
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General Rules
• Hund’s Rule
– Within a sublevel, place one electron
per orbital before pairing them.
– “Empty Bus Seat Rule”
WRONG
RIGHT
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8
O
Notation
15.9994
• Orbital Diagram
O
8e-
2s
1s
2p
• Electron Configuration
1s2 2s2 2p4
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Notation
S
32.066
• Longhand Configuration
S 16e- 1s2 2s2 2p6 3s2 3p4
Core Electrons
Valence Electrons
• Shorthand Configuration
S 16e-
[Ne] 3s2 3p4
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Periodic Patterns
s
1
2
3
4
5
6
7
p
1s
2s
1s
2p
3s
d (n-1)
3p
4s
3d
4p
5s
4d
5p
6s
5d
6p
7s
6d
7p
6
4f
f (n-2) 7
5f
Periodic Patterns
• Period #
– energy level (subtract for d & f)
• A/B Group #
– total # of valence e-
• Column within sublevel block
– # of e- in sublevel
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Periodic Patterns
• Example - Hydrogen
1
2
3
4
5
6
7
1st column
of s-block
1s1
1st Period
s-block
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Periodic Patterns
• Shorthand Configuration
– Core electrons:
• Go up one row and over to the Noble Gas.
– Valence electrons:
• On the next row, fill in the # of e- in each sublevel.
1
2
3
4
5
6
7
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Periodic Patterns
Ge
72.61
• Example - Germanium
1
2
3
4
5
6
7
[Ar] 4s2 3d10 4p2
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Stability
• Full energy level
• Full sublevel (s, p, d, f)
• Half-full sublevel
1
2
3
4
5
6
7
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The Octet Rule
Atoms tend to gain, lose, or share electrons
until they have eight valence electrons.
This fills the valence
shell and tends to give
the atom the stability
of the inert gasses.
8
ONLY s- and p-orbitals are valence electrons.
Write out the complete electron configuration for the following:
1) An atom of nitrogen
2) An atom of silver
3) An atom of uranium (shorthand)
POP
QUIZ
Fill in the orbital boxes for an atom of nickel (Ni)
1s
2s
2p
3s
3p
4s
3d
Which rule states no two electrons can spin the same direction in a single orbital?
Extra credit: Draw a Bohr model of a Ti4+ cation.
Ti4+ is isoelectronic to Argon.
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Answer Key
Write out the complete electron configuration for the following:
1) An atom of nitrogen 1s22s22p3
1s22s22p63s23p64s23d104p65s24d9
2) An atom of silver
3) An atom of uranium (shorthand)
[Rn]7s26d15f3
Fill in the orbital boxes for an atom of nickel (Ni)
1s
2s
2p
3p
3s
4s
3d
Which rule states no two electrons can spin the same direction in a single orbital?
Pauli exclusion principle
Extra credit: Draw a Bohr model of a Ti4+ cation.
n=
22+
n
Ti4+ is isoelectronic to Argon.
Electron Configurations
of First 18 Elements:
Hydrogen
1H
Helium
2He
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
3Li
4Be
5B
6C
7N
8O
9F
10Ne
Sodium
Magnesium
Aluminum
Silicon
Phosphorous
Sulfur
Chlorine
Argon
11Na
12Mg
13Al
14Si
15P
16S
17Cl
18Ar
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Electron Dot Diagrams
Group
1A
1
2A
2
3A
13
4A
14
5A
15
6A
16
7A
17
H
8A18
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Ga
Ge
As
Se
Br
Kr
s1
s2
s2p1
s2p2
s2p3
s2p4
s2p5
s2p6
= valence electron
V. Outer Level e-’s
• Valence electrons
• Usually involved in chemical
changes
• Dot diagram
–Symbol represents the nucleus
–Dots represent the outer e-’s
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