Transcript General Chemistry CHEM 103

Chapter 8
Atomic Electron Configurations
and Chemical Periodicity
Dr. S. M. Condren
ATOMIC ELECTRON
CONFIGURATIONS AND
PERIODICITY
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Atomic Orbitals
• Types of orbitals found in the known
elements: s, p, d, and f
• schools play defensive football
• Packer version: secondary pass defense
fails
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Atomic Orbitals
Shapes
• s – spherical
• p – dumbbell
• d – complex
• f – very complex
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Arrangement of Electrons in Atoms
Electrons in atoms are arranged as
SHELLS (n)
SUBSHELLS (l)
ORBITALS (ml)
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Arrangement of Electrons in Atoms
Each orbital can be assigned no
more than 2 electrons!
This is tied to the existence of a 4th
quantum number, the electron
spin quantum number, ms.
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Electron
Spin
Quantum
Number,
ms
Can be proved experimentally that electron
has a spin. Two spin directions are given by
ms where ms = +1/2 and -1/2.
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Electron Spin and Magnetism
•Diamagnetic: NOT
attracted to a magnetic
field
•Paramagnetic:
substance is attracted to
a magnetic field.
•Substances with
unpaired electrons are
paramagnetic.
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Measuring Paramagnetism
Paramagnetic: substance is attracted to a
magnetic field. Substance has unpaired electrons.
Diamagnetic: NOT attracted to a magnetic field
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Active
Figure 8.2
QUANTUM NUMBERS
Now there are four!
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
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Pauli Exclusion Principle
No two electrons in the same
atom can have the same set
of 4 quantum numbers.
That is, each electron has a
unique address.
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Electrons in Atoms
When n = 1, then l = 0
this shell has a single orbital (1s) to which
2e- can be assigned
When n = 2, then l = 0, 1
2s orbital
three 2p orbitals 6eTOTAL =
8e-
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2e-
Electrons in Atoms
When n = 3, then l = 0, 1, 2
3s orbital
three 3p orbitals
five 3d orbitals
TOTAL =
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2e6e10e18e-
Electrons in Atoms
When n = 4, then l = 0, 1, 2, 3
4s orbital
three 4p orbitals
five 4d orbitals 10eseven 4f orbitals
TOTAL =
2e6e14e32e-
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And many more!
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Assigning Electrons to Atoms
• Electrons generally assigned to
orbitals of successively higher
energy.
• For H atoms, E = - C(1/n2). E
depends only on n.
• For many-electron atoms, energy
depends on both n and l.
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Electron
Filling
Order
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LED Traffic Lights
http://mrsec.wisc.edu/Edetc/background/LED/traffic_light/index.htm
Chapter 7, Problem 3, page 326 text
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Writing Atomic Electron Configurations
Two ways of
writing configs.
One is called the
spdf notation.
spdf notation
for H, atomic number = 1
1
1s
value of n
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no. of
electrons
value of l
Writing Atomic Electron Configurations
Other is called the
orbital box notation
ORBITAL BOX NOTATION
for He, atomic number = 2
2
1s
1s
Arrows
depict
electron
spin
One electron has n = 1, l = 0, ml = 0, ms = + 1/2
Other electron has n = 1, l = 0, ml = 0, ms = - 1/2
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See “Toolbox” on CD for Electron Configuration tool.
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Electron Configurations
and the Periodic Table
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Lithium
3p
Group 1A
Atomic number = 3
1s22s1 --->
3 total electrons
3s
2p
2s
1s
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Beryllium
3p
3s
Group 2A
Atomic number = 4
1s22s2 --->
4 total electrons
2p
2s
1s
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Boron
3p
3s
Group 3A
Atomic number = 5
1s2 2s2 2p1 --->
5 total electrons
2p
2s
1s
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Carbon
Group 4A
Atomic number = 6
1s2 2s2 2p2 --->
6 total electrons
3p
3s
2p
2s
1s
Here we see for the first time
HUND’S RULE. When
placing electrons in a set of
orbitals having the same
energy, we place them singly
as long as possible.
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Nitrogen
3p
3s
Group 5A
Atomic number = 7
1s2 2s2 2p3 --->
7 total electrons
2p
2s
1s
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Oxygen
3p
3s
Group 6A
Atomic number = 8
1s2 2s2 2p4 --->
8 total electrons
2p
2s
1s
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Fluorine
3p
3s
Group 7A
Atomic number = 9
1s2 2s2 2p5 --->
9 total electrons
2p
2s
1s
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Neon
3p
3s
2p
2s
1s
Group 8A
Atomic number = 10
1s2 2s2 2p6 --->
10 total electrons
Note that we have
reached the end of
the 2nd period, and
the 2nd shell is full!
Dr. S. M. Condren
Sodium
Group 1A
Atomic number = 11
1s2 2s2 2p6 3s1 or
“neon core” + 3s1
[Ne] 3s1 (uses rare gas notation)
Note that we have begun a new period.
All Group 1A elements have [core]ns1
configurations.
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Aluminum
Group 3A
Atomic number = 13
1s2 2s2 2p6 3s2 3p1
[Ne] 3s2 3p1
All Group 3A elements
have [core] ns2 np1
configurations where n
is the period number.
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3p
3s
2p
2s
1s
Phosphorus
Yellow P
Group 5A
Atomic number = 15
1s2 2s2 2p6 3s2 3p3
[Ne] 3s2 3p3
All Group 5A elements
have [core ] ns2 np3
configurations where n
is the period number.
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Red P
3p
3s
2p
2s
1s
Calcium
Group 2A
Atomic number = 20
1s2 2s2 2p6 3s2 3p6 4s2
[Ar] 4s2
All Group 2A elements have [core]ns2
configurations where n is the period
number.
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Transition Metals Table 8.4
All 4th period elements have the
configuration [argon] nsx (n - 1)dy
and so are d-block elements.
Chromium
Iron
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Copper
Transition Element Configurations
3d orbitals used for
Sc-Zn (Table 8.4)
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Board Work
•
•
•
•
•
•
V – electron configuration
Cr – electron configuration
Mn – electron configuration
Ni – electron configuration
Cu – electron configuration
Zn – electron configuration
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Magnetism
Paramagnetism
Spins are aligned with or against
an applied magnetic field.
Spins are randomized by thermal energy.
Ferromagnetism
Spins are aligned with an
applied magnetic field.
Spins are ordered in magnetic domains.
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NMR and MRI
Nuclei also have spin and nuclear quantum numbers
800 MHz, 18.8 T NMR spectrometer
Open Magnet Design MRI
http://mrsec.wisc.edu/Edetc/background/NMR/index.html
http://mrsec.wisc.edu/Edetc/cineplex/NMR/index.html
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Memory Metal
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Nitinol, NiTi
http://mrsec.wisc.edu/Edetc/background/memmetal/index.html
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Lanthanides and Actinides
All these elements have the configuration [core]
nsx (n - 1)dy (n - 2)fz and so are
f-block elements.
Cerium
[Xe] 6s2 5d1 4f1
Uranium
[Rn] 7s2 6d1 5f3
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Lanthanide Element Configurations
4f orbitals used for Ce - Lu
and 5f for Th - Lr (Table 8.2)
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Ion Configurations
To form cations from elements remove 1 or
more e- from subshell of highest n [or highest
(n + l)].
P [Ne] 3s2 3p3 - 3e- ---> P3+ [Ne] 3s2 3p0
3p
3p
3s
3s
2p
2p
2s
2s
1s
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1s
Ion Configurations
For transition metals, remove ns electrons and
then (n - 1) electrons.
Fe [Ar] 4s2 3d6
loses 2 electrons ---> Fe2+ [Ar] 4s0 3d6
Fe2+
Fe
4s
4s
3d
To form cations, always remove
electrons of highest n value first!
3d
Fe3+
4s
3d
http://mrsec.wisc.edu/Edetc/cineplex/ff/index.html
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Quantum Numbers
What is one of the sets of quantum numbers
for the 4s electrons in calcium?
n = 4; l = 0; ml = 0; s = +1/2 or
n = 4; l = 0; ml = 0; s = -1/2
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Quantum Numbers
What is one of the sets of quantum numbers
for the 3p electrons in sulfur?
n = 3; l = 1; ml = +1; s = +1/2 or
n = 3; l = 1; ml = +1; s = -1/2 or
n = 3; l = 1; ml = 0; s = +1/2 or
n = 3; l = 1; ml = 0; s = -1/2
or
n = 3; l = 1; ml = -1; s = +1/2 or
n = 3; l = 1; ml = -1; s = -1/2
Dr. S. M. Condren
Quantum Numbers
What is one of the sets of quantum numbers
for the 3d electrons in Fe?
n = 3; l = 2; ml = +2; s = +1/2 or n = 3; l = 2; ml = +2; s = -1/2
or n = 3; l = 2; ml = +1; s = +1/2 or n = 3; l = 2; ml = +1; s = -1/2
or n = 3; l = 2; ml = 0; s = +1/2
or n = 3; l = 2; ml = 0; s = -1/2
or n = 3; l = 2; ml = -1; s = +1/2
or n = 3; l = 2; ml = -1; s = -1/2
or n = 3; l = 2; ml = -2; s = +1/2
or n = 3; l = 2; ml = -2; s = -1/2
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Announcements
• You may bring a 4x6 index card with
information
• A periodic table and a table of
thermodynamic data will be furnished.
• You need to know your TAs name and
your section number.
• Photo ID will be required when submitting
your exam.
Dr. S. M. Condren
Announcements
Teaching Assistant _________________________ Section _____ Name _________________________________ c
General Chemistry 103
Hour Exam 2
Nov. 6, 2006
ALL WORK MUST APPEAR ON TEST FOR ANY CREDIT.
Work includes “stating the question in a mathematical form.”
A box should be drawn around the answer to be graded for a problem.
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Announcements
• Last day to drop
• Suzie and Christie have papers to return,
please see them after class
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Bonus Points
• Exam II – worth 105 points, count as 100
• 5 pts - Available through “Other Lecture
Documents” this week, due Friday Nov. 10
• Exam III – worth 105 points, count as 100
• 5 pts - Available through “Other Lecture
Documents” later, due Friday Dec. 15
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Ion Configurations
How do we know the configurations of ions?
Determine the magnetic properties of ions.
Sample
of Fe2O3
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Sample
of Fe2O3
with
strong
magnet
General Periodic Trends
• Atomic and ionic size
• Ionization energy
• Electron affinity
Higher effective nuclear charge
Electrons held more tightly
Larger orbitals.
Electrons held less
tightly.
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Effective Nuclear Charge, Z*
• Atom
•
•
•
•
•
•
•
Li
Be
B
C
N
O
F
Z* Experienced by Electrons in
Valence Orbitals
+1.28
------Increase in
+2.58
Z* across a
+3.22
+3.85
period
+4.49
+5.13
[Values calculated using Slater’s Rules]
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Orbital Energies
Orbital energies “drop” as Z* increases
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Atomic Radii
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Atomic Size
• Size goes UP on going down a group.
• Because electrons are added further from
the nucleus, there is less attraction.
• Size goes DOWN on going across a
period.
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Atomic Radius
Size decreases across a period
owing to increase in Z*. Each added
electron feels a greater and greater
+ charge.
Large
Small
Increase in Z*
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Trends in Atomic Size
Radius (pm)
250
K
1st transition
series
3rd period
200
Na
2nd period
Li
150
Kr
100
Ar
Ne
50
He
0
0
5
10
15
20
Atomic Number
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25
30
35
40
Sizes of Transition Elements
3d subshell is
inside the 4s
subshell.
4s electrons feel a
more or less
constant Z*.
Sizes stay about the
same and
chemistries are
similar!
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Density of Transition Metals
25
20
6th period
Density (g/mL)
15
10
5th period
4th period
5
0
3B
4B
5B
6B
7B
8B
Group
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1B
2B
Ion Sizes
Li,152 pm
3e and 3p
Does the size go
+
up or down
when
Li + , losing
60 pm an
electron
2e and to
3 pform
a cation?
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Ion Sizes
+
Li,152 pm
3e and 3p
Li + , 78 pm
2e and 3 p
Forming
a cation.
• CATIONS are SMALLER than the
atoms from which they come.
• The electron/proton attraction has
gone UP and so size DECREASES.
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Ion Sizes
Does the size go up
or down when
gaining an electron to
form an anion?
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Ion Sizes
F, 71 pm
9e and 9p
Forming
an anion.
F- , 133 pm
10 e and 9 p
• ANIONS are LARGER than the atoms
from which they come.
• The electron/proton attraction has gone
DOWN and so size INCREASES.
• Trends in ion sizes are the same as atom
sizes.
Dr. S. M. Condren
Trends in Ion Sizes
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Trends in Ionization Energy
1st Ionization energy (kJ/mol)
2500
He
Ne
2000
Ar
1500
Kr
1000
500
0
1
H
3
Li
5
7
9
11
Na
13
15
17
19
21
K
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23
25
27
29
31
Atomic Number
33
35
Electron Affinity
A few elements GAIN electrons
to form anions.
Electron affinity is the energy
involved when an atom gains
an electron to form an anion.
A(g) + e- ---> A-(g)
E.A. = ∆E
Dr. S. M. Condren
Electron Affinity of Oxygen
O atom [He] 
 

+ electron
O- ion [He] 
 

∆E is EXOthermic
because O has
an affinity for an
e-.
EA = - 141 kJ
Dr. S. M. Condren
Electron Affinity of Nitrogen
N atom [He] 
 

+ electron
N- ion
[He] 


EA = 0 kJ

∆E is zero for
N- due to
electronelectron
repulsions.
Dr. S. M. Condren
Announcements
• You may bring a 4x6 index card with
information
• A periodic table and a table of
thermodynamic data will be furnished.
• You need to know your TAs name and
your section number.
• Photo ID will be required when submitting
your exam.
Dr. S. M. Condren
Announcements
• Last day to drop
• Suzie and Christie have papers to return,
please see them after class
Dr. S. M. Condren