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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