ch 8: electron configuration renee y. becker valencia community college chm 1045 1
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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)
NOT __
3px 3py 3pz
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Electron Configuration of Atoms
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 7s 7p
Increasing Energy
[He][Ne] [Ar] [Kr] [Xe] [Rn]
Core
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Electron Configuration of Atoms
Element Diagram Configuration
Li (Z = 3) 1s2 2s1
1s 2s
Be (Z = 4) 1s2 2s2 1s 2s
B (Z = 5) __ __ 1s2 2s2 2p1
1s 2s 2px 2py 2pz
C (Z = 6) __ 1s2 2s2 2p2
1s 2s 2px 2py 2pz
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Electron Configuration of Atoms
Element Diagram Configuration
O (Z = 8) 1s2 2s2 2p4
1s 2s 2px 2py 2pz
Ne (Z = 10) 1s2 2s2 2p6
1s 2s 2px 2py 2pz
S (Z = 16) 1s 2s 2px 2py 2pz 3s 3px 3py 3pz
1s2 2s2 2p6 3s2 3p6 or [Ne] 3s2 3p6
abbreviations using the noble gases valence vs. core electrons
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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 11
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 O2-
5.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- 15
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: 1s2 2s2 2p6 3s2 3p1 = [Ne] 3s2 3p1
– Al3+ 1s2 2s2 2p6 = [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. Cl-
2. F-
3. 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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