Electron Configuration

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Electron Configuration
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Order of Energy Levels

• Inner shell electrons shield outer electrons
  from the full positive effect of the nucleus
  screening effect
• Different orbitals shield the outer electrons
  more effectively than others
• Not all orbitals experience the same charge
  from the nucleus
• Therefore different orbitals have different
  potential energies

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Degenerate Orbitals

• Orbitals that have the same energies

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Electron Spin

• Electron behaves as if it is spinning on its axis
• Fourth Quantum number (ms) is the spin number
• It can be either 1/2 or 1/2

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• Spinning electrons produce magnetic fields

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Pauli Exclusion Principle

• No two electrons can have the same set of four
  quantum numbers (n, l, ml, ms)
• If an orbital has two electrons in it, they must
  have different spins
• Electrons in the same orbital with different
  spins are called paired electrons

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Configuration

• Arrangement of electrons in the atom
• Aufbau Principle orbitals fill in order of
  increasing energy

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Orbital Diagram of Li ( 3 e-)

• 1s22s1

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Orbital Diagram of B (5 e-)

• 1s22s22p1

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Hunds Rule

• Electrons occupy degenerate orbits singly first

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Orbital Diagram of C (6 e-)

• 1s22s22p2

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Orbital Diagram of Ne (10 e-)

• Configuration 1s22s22p6

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Valence Electrons

• Outer shell electrons
• Ones in the last main energy level
• ? K 1s22s22p63s23p64s1 1 valence e
• Fe 1s22s22p63s23p64s23d6 2 valence e