Transcript CH 8: Electron Configuration

CH 8: Electron Configuration
Renee Y. Becker
Valencia Community College
CHM 1045
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Electron Configuration of Atoms
Rules of Aufbau Principle:
• Lower n orbitals fill first.
• Each orbital holds two electrons; each with
different ms.
• Half-fill degenerate orbitals before pairing
electrons. (p, d, & f)
  
3px 3py 3pz
NOT 

__
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Electron Configuration of Atoms
Increasing Energy
Core
[He]
[Ne]
[Ar]
[Kr]
[Xe]
[Rn]
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
7p
3d
4d 4f
5d 5f
6d
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Electron Configuration of Atoms
Element
Diagram
Configuration
Li (Z = 3)
 
1s 2s
1s2 2s1
Be (Z = 4)
 
1s 2s
1s2 2s2
B (Z = 5)
   __ __
1s 2s 2px 2py 2pz
1s2 2s2 2p1
C (Z = 6)
    __
1s 2s 2px 2py 2pz
1s2 2s2 2p2
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Electron Configuration of Atoms
Element
O (Z = 8)
Diagram
 
1s 2s
Ne (Z = 10)  
1s 2s
S (Z = 16)
 
1s 2s
Configuration
  
2px 2py 2pz
1s2 2s2 2p4
  
2px 2py 2pz
1s2 2s2 2p6
     

2px 2py 2pz 3s 3px 3py 3pz
1s2 2s2 2p6 3s2 3p6
or
abbreviations using the noble gases
valence vs. core electrons
[Ne] 3s2 3p6
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Electron Configuration of Atoms
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Electron Configuration of Atoms
Tc (Z = 43) [Kr] 5s2 4d5
Technetium
Ni (Z = 28) [Ar] 4s2 3d8
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Electron Configuration of Atoms
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Electron Configuration of Atoms
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Example 1: Electron Config. And NG Abb.
1. Sodium
2. Titanium
3. Argon
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Anomalous Electron Configurations
• 19 of the predicted configurations from the
periodic table are wrong
– Largely due to unusual stability of both half-filled
and fully filled subshells
Cr (Z=24)
expected configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d4
     __
4s 3d 3d 3d 3d 3d
actual configuration:
1s2 2s2 2p6 3s2 3p6 4s1 3d5
    

4s 3d 3d 3d 3d 3d
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Atomic Radii
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Atomic Radii
• ½ the distance between the nuclei of
two identical atoms when they are
bonded together.
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Example 2: Ionic Radii
Which of the following in each pair has a larger
atomic radius?
1. Carbon or Fluorine
2. Chlorine or Iodine
3. Sodium or Magnesium
4. O or O25. Ca or Ca2+
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Example 3: Quantum Numbers and Electron Configuration
What are the 4 quantum numbers for the
following? Remember you are only interested
in the last electron!!
1. C
2. Na+
3. S
4. N3-
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Main Groups
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Ions and their Electron Configuration
• Main-group metals donate electrons from the
atom’s highest-energy occupied atomic
orbital.
– Na:
1s2 2s2 2p6 3s1
= [Ne] 3s1
– Na+:
1s2 2s2 2p6
= [Ne]
– Mg:
1s2 2s2 2p6 3s2
= [Ne] 3s2
– Mg2+:
1s2 2s2 2p6
= [Ne]
– Al:
– Al3+
1s2 2s2 2p6 3s2 3p1
1s2 2s2 2p6
= [Ne] 3s2 3p1
= [Ne]
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Ions and their Electron Configuration
• Main-group nonmetals accept electrons into
their lowest-energy unoccupied atomic
orbital.
– N:
1s2 2s2 2p3
= [He] 2s2 2p3
– N3–:
1s2 2s2 2p6
= [He] 2s2 2p6 = [Ne]
– O:
1s2 2s2 2p4
= [He] 2s2 2p4
– O2–:
1s2 2s2 2p6
= [He] 2s2 2p6 = [Ne]
– F:
1s2 2s2 2p5
= [He] 2s2 2p5
– F–:
1s2 2s2 2p6
= [He] 2s2 2p6 = [Ne]
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Example 4: Electron config. and NG Abb.
1. Cl2. F3. Ca2+
4. Na+
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Ionic Radii or size
• Atoms shrink when an electron is
removed to form a cation
– Dec. # of shells
– Inc. Zeff : Less electrons, less shielding,
outer electrons more attracted to nucleus,
therefore smaller more compact
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Ionic Radii or size
• Atoms expand when converted to anions
– III A ns2 np1
__ __ __
– IV A ns2 np2
__ __ __
– V A ns2 np3
__ __ __
– VI A ns2 np4
__ __ __
– VII A ns2 np5
__ __ __
Adding one electron to each of these will not
add another shell it will just fill an already
occupied p subshell
• Therefore the expansion is due to the
decrease in Zeff and the increase in the
electron-electron repulsions
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Ionization Energy, Ei
• The amount of energy needed to remove the highest-energy
electron from an isolated neutral atom in the gaseous state
Increase
Increase
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Ionization Energy, Ei
• Some exceptions/irregularities to general
trend
– Ei Be > Ei B we would expect opposite
– Be 4 e 1s2 2s2
– B 5 e 1s2 2s2 2p1
• 2s is closer to nucleus than 2p, Zeff for
Be is stronger
• 2s is held more tightly and is harder to
remove
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Ionization Energy, Ei
• Ei N > Ei O we would expect opposite
• N 7e 1s2 2s2 2p3
__ __ __
• O 8e 1s2 2s2 2p4
__ __ __
• Only difference is that an electron is being removed
from a half-filled orbital (N) and one from a filled
orbital (O)
– Electrons repel each other and tend to stay as far apart as
possible, electrons that are forced together in a filled orbital
are slightly higher in energy so it is easier to remove one
• Therefore O < N
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Higher Ionization Energy, Ei1234…
• Ionization is not limited to one electron
M + Energy  M+ + e
Ei1
M+ + Energy  M2+ + e
Ei2
M2+ + Energy  M3+ + e Ei3
• Larger amts. Of energy are needed for each
successive ionization, harder to remove an
electron from a positively charger cation
• The energy differences between successive
steps vary from one element to another.
Why? EC
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Higher Ionization Energy, Ei1234…
• Easy to remove an electron from a partially filled
valence shell
• Difficult to remove an electron from a filled valence
shell
• Large amount of stability associated with filled s & p
subshells
• Na:
1s2 2s2 2p6 3s1
• Mg:
1s2 2s2 2p6 3s2
• Cl:
1s2 2s2 2p6 3s2 3p5
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Electron Affinity, Eea
• Energy change that occurs when an electron
is added to an isolated atom in the gaseous
state.
• The more neg. the Eea the greater the
tendency of the atom to accept an electron
• Group 7A (halogens) have the most neg. Eea,
high Zeff and room in valence shell
• Group 2A and 8A have near zero or slightly
positive Eea
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Alkali Metals
• Group 1A
– Metallic
– Soft
– Good Conductors
– Low MP
– Lose 1 elec in redox, powerful reducing agent
– Very reactive
– Not found in elemental state in nature
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Alkaline Earth Metals
• Group 2A
– Harder, but still relatively soft
– Silvery
– High MP than group 1A
– Less reactive than group 1A
– Lose 2 e in redox, powerful reducing agent
– Not found in elemental form in nature
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Group 3A
• All but Boron
– Silvery
– Good conductor
– Relatively soft
– Less reactive than 1A & 2A
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Halogens
• Group 7A
– Non-metals
– Diatomic molecules
– Tend to gain e during redox
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Noble Gases
• Group 8A
– Colorless, odorless, unreactive gases
– Ns2 np6
• Makes it difficult to add e or remove e
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Octet Rule
• Group 1A tends to lose their ns1
valence shell electron to adopt a noble
gas electron config.
• Group 2A lose both ns2 “ “
• Group 3A lose all three ns2 np1 “ “
• Group 7A Gains one electron to attain
NG
• Group 8A inert, rarely lose or gain
electrons
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