Modern Chemistry
Chapter 4
Arrangement of Electrons
in Atoms
Sections 1-3
The Development of a New Atomic Model
The Quantum Model of the Atom
Electron Configurations
1
Section 2
The Quantum Model
of the Atom
Chapter 4 Section 2 The Quantum
Model pages 104-110
2
Electrons As Waves
• Electrons can have wave and particle
characteristics (like light).
• Waves (electrons) confined to a space
can have only certain frequencies
• The frequencies correspond
to Bohr’s orbits.
– Louis de Broglie
Chapter 4 Section 2 The Quantum
Model pages 104-110
3
Electrons As Waves
• This is confirmed by experiments
• Electrons, like waves, can be bent,
diffracted and have interference
• Diffraction: the bending of a wave as it
passes through a small
opening
• Interference: when
waves overlap.
Chapter 4 Section 2 The Quantum
Model pages 104-110
4
The Heisenberg Uncertainty Principle
• Involves the detection of electrons
• To detect an electron a photon is used
• The photon interacts with the electron
and changes its course
• There is uncertainty in trying to locate
an electron.
Chapter 4 Section 2 The Quantum
Model pages 104-110
5
The Heisenberg Uncertainty Principle
• It is impossible to determine
simultaneously both the position and
velocity of an electron or any other
particle.
Chapter 4 Section 2 The Quantum
Model pages 104-110
6
The Schrödinger Wave Equation
• Developed an equation that treats
electrons as waves
• Proved the quantization of electron
energies
• Quantum theory: describes
mathematically the wave
properties of electrons
and other small particles
Chapter 4 Section 2 The Quantum
Model pages 104-110
7
The Schrödinger Wave Equation
• Solutions to the equations are wave
functions.
• Wave functions give the probability of
finding electrons.
• Electrons do not travel in neat orbits.
• Electrons exist in regions called orbitals.
• Orbital: a three dimensional region
around the nucleus that indicates the
probable location of electrons.
Chapter 4 Section 2 The Quantum
Model pages 104-110
8
Heisenbery Uncertainty
Principle Animation
Chapter 4 Section 2 The Quantum
Model pages 104-110
9
Atomic Orbitals and Quantum Numbers
• Quantum numbers specify the properties
of atomic orbitals and the properties of
electrons in the orbital.
• The first three numbers result from the
solution to Schrodinger’s wave equation.
Chapter 4 Section 2 The Quantum
Model pages 104-110
10
Principle Quantum Number
• Symbol = n
• Energy Level
• n = 1, 2, 3, 4, 5, 6, 7 (whole numbers)
• As n increases the electron’s energy and
average distance from the nucleus
increases.
Chapter 4 Section 2 The Quantum
Model pages 104-110
11
Angular Momentum
Quantum Number
• Symbol = l
• Shape of orbital (sublevel)
• l = s, p, d, f
• A sublevel is made up of a certain
number of orbitals
Chapter 4 Section 2 The Quantum
Model pages 104-110
12
Atomic Orbitals and Quantum Numbers
Sublevel Orbitals Electrons
s
1
2
p
3
6
d
5
10
f
7
14
Chapter 4 Section 2 The Quantum
Model pages 104-110
13
Magnetic Quantum Number
• Symbol = m
• Orientation around the nucleus
• m = x, y, z, xy, yz, xz
Chapter 4 Section 2 The Quantum
Model pages 104-110
14
Spin Quantum Number
• Symbol = ms
• Spin State of the electron
• m = +1/2, -1/2
• When electrons spin they produce a
magnetic field.
• Two electrons can exist in one orbital.
• Each electron must have an opposite
spin state.
Chapter 4 Section 2 The Quantum
Model pages 104-110
15
7s2
7p6
7d10
7f14 7g 7h 7i
6s2
6p6
6d10
6f14 6g 6h
5s2
5p6
5d10
5f14 5g
4s2
4p6
4d10
4f14
3s2
3p6
3d10 18e- = 2 + 6 + 10
2s2
2p6 8e- = 2 + 6
1s2 2e- = 2 in the s orbital
Chapter 4 Section 2 The Quantum
Model pages 104-110
# of electrons
on a
energy level
32e- = 2+6+10+14
Section 3
Electron
Configurations
Chapter 4 Section 3 Electron
Configurations pages 110-122
17
Section 3 Vocabulary
Electron configuration
Aufbau principle
Pauli exclusion principle
Hund’s Rule
Noble Gas
Noble Gas configurations
Chapter 4 Section 3 Electron
Configurations pages 110-122
18
Rules Governing Electron Configurations
• Aufbau Principle
– An electron occupies the lowest energy
orbital that can receive it
– Less energy is required for electrons to pair
up in the 4s than the 3d.
– Aufbau:
German for construction
Chapter 4 Section 3 Electron
Configurations pages 110-122
19
Aufbau Principle Animation
p. 111
Chapter 4 Section 3 Electron
Configurations pages 110-122
20
Rules Governing Electron Configurations
• Pauli Exclusion Principle
– No two electrons in the same atom can
have the same set of four quantum
numbers.
– Electrons must have opposite spin states
– Two electrons can exist
in an orbital.
Chapter 4 Section 3 Electron
Configurations pages 110-122
22
Pauli and Bohr
Chapter 4 Section 3 Electron
Configurations pages 110-122
23
Rules Governing Electron Configurations
• Hund’s Rule
– Orbitals of equal energy are each occupied
by one electron before any orbital is
occupied by a second electron, and
all electrons in singly occupied orbitals must
have the same spin state.
– Repulsion between
electrons is minimized.
Chapter 4 Section 3 Electron
Configurations pages 110-122
25
Chapter 4 Section 3 Electron
Configurations pages 110-122
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
6d
4f
5f
Chapter 4 Section 3 Electron
Configurations pages 110-122
PRACTICE
p. 113
1. Page 113 # 1 & 2
2. Write the electron configurations for the
following elements: Ne, Na, Mg, Ar, K
Chapter 4 Section 3 Electron
Configurations pages 110-122
28
Orbital Notation Animation
Chapter 4 Section 3 Electron
Configurations pages 110-122
29
Representing Electron Configurations
• Orbital Notation
     .
1s 2s 2p
– Which element is this?
– How does this show Hund’s rule?
Chapter 4 Section 3 Electron
Configurations pages 110-122
30
Orbital Diagram for Si
orbital
14 electrons
electron
(-1/2 spin)
1s
2s 2p
3s
3p
electron
sublevel
(+1/2 spin)
Chapter 4 Section 3 Electron
Configurations pages 110-122
Shapes of s, p and d orbitals
Image
p.108
Chapter 4 Section 3 Electron
Configurations pages 110-122
32
Representing Electron Configurations
• Orbital Notation
     .
1s 2s 2p
• Electron Configurations
1s2 2s2 2p3
– Use superscripts instead of lines and
arrows.
Chapter 4 Section 3 Electron
Configurations pages 110-122
33
Reading Electron Configuration
Notation Animation
Chapter 4 Section 3 Electron
Configurations pages 110-122
34
Electron Configurations
For Manganese – 25 electrons
2
2
6
2
6
2
1s 2s 2p 3s 3p 4s 3d
sublevel
number of
electrons in
the sublevel
Chapter 4 Section 3 Electron
Configurations pages 110-122
5
Electron Configuration
Animation
p. xx
Chapter 4 Section 3 Electron
Configurations pages 110-122
36
PRACTICE
p. 113
1. Page 113 # 1 & 2
2. Write the electron configurations for the
following elements: Ne, Na, Mg, Ar, K
Chapter 4 Section 3 Electron
Configurations pages 110-122
37
Elements of the Second Period
2 2s1
Li
=
1s
3
2 2s2 2p2
C
=
1s
6
Inner shell
electrons
Highest occupied energy level
C = 4 valence electrons
Li = 1 valence electron
Valence electrons: electrons occupying the
highest energy level in an atom
Chapter 4 Section 3 Electron
Configurations pages 110-122
38
Elements of the Third Period
10Ne
=
2 2s2 2p6 3s1
1s
11Na =
2 2s2 2p6 3s2
1s
Mg
=
12
2 2s2 2p6 3s2 3p6
Ar
=
1s
18
2 2s2 2p6 3s2 3p6 4s1
K
=
1s
19
1s2 2s2 2p6
Chapter 4 Section 3 Electron
Configurations pages 110-122
Elements of the Third Period
10Ne
Look! It’s
neon!
=
2 2s2 2p6 3s1
1s
11Na =
2 2s2 2p6 3s2
1s
Mg
=
12
2 2s2 2p6 3s2 3p6
Ar?!
Ar
=
1s
18
2 2s2 2p6 3s2 3p6 4s1
K
=
1s
19
1s2
2s2
2p6
Chapter 4 Section 3 Electron
Configurations pages 110-122
Elements of the Third Period
10Ne
=
2 2s2 2p6 3s1
1s
[Ne]
11Na =
2 [Ne]
2 2p6 3s2
1s
2s
Mg
=
12
2 2s2 2p6 3s2 3p6
Ar
=
1s
18
2 2s2 [Ar]
6 3s2 3p6 4s1
K
=
1s
2p
19
1s2 2s2 2p6
Chapter 4 Section 3 Electron
Configurations pages 110-122
Elements of the Third Period
10Ne
=
1
[Ne]
3s
11Na =
2
[Ne]
3s
Mg
=
12
2 2s2 2p6 3s2 3p6
Ar
=
1s
18
1
K
=
[Ar]
4s
19
1s2 2s2 2p6
Chapter 4 Section 3 Electron
Configurations pages 110-122
Noble Gas Notation Animation
Chapter 4 Section 3 Electron
Configurations pages 110-122
43
Noble Gas Configuration
1. Find the noble gas with an atomic
number closest to but less than the
element’s atomic number.
2. Find the next sublevel after that noble
gas
3. Fill in sublevels with the “leftover”
electrons.
(atomic # of element – atomic # of noble gas)
Chapter 4 Section 3 Electron
Configurations pages 110-122
44
Noble Gas Configurations
1s2
2p6
3p6
4p6
5p6
6p6
Chapter 4 Section 3 Electron
Configurations pages 110-122
Chapter 4 Section 3 Electron
Configurations pages 110-122
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
6d
4f
5f
Chapter 4 Section 3 Electron
Configurations pages 110-122
Elements of the Fourth Period
• Deviations
– 24Cr = [Ar] 4s2 3d4 WRONG!!!
– 24Cr = [Ar] 3d5 4s1
– unpaired electrons give
a more stable arrangement with
a lower energy
– 29Cu = [Ar] 3d9 4s2 WRONG!!!
– 29Cu = [Ar] 3d10 4s1
– No explanation for either
Chapter 4 Section 3 Electron
Configurations pages 110-122
48
Elements of the Fourth Period
• Even though the d sublevel fills before
the p sublevel, the s sublevel is moved
to be with the p sublevel.
• 53I = [Kr] 5s2 4d10 5p5 is written as…
• 53I = [Kr] 4d10 5s2 5p5
• The sublevels on the same energy level
are together.
• It also shows the valence electrons.
Chapter 4 Section 3 Electron
Configurations pages 110-122
49
Elements of the Fifth Period
p.120
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
[Kr]
[Kr]
[Kr]
[Kr]
[Kr]
[Kr]
[Kr]
[Kr]
[Kr]
[Kr]
4d1 5s2
4d2 5s2
4d43 5s12
4d45 5s21
4d65 5s12
4d67 5s21
4d87 5s12
8 5s2
4d10
9 5s21
4d10
5s
4d10 5s2
Chapter 4 Section 3 Electron
Configurations pages 110-122
expected
deviations
expected
50
Elements of the Sixth Period
• 4f and 5d are very close in energy
causing many deviations
• Look at the configurations on the
periodic table on the back cover of the
book.
Chapter 4 Section 3 Electron
Configurations pages 110-122
52
Section 3 Homework
Chapter 4 Section 3 Electron
Configurations pages 110-122
54