Notes: Electron Configurations (Sect 5.3)

Topics:

• Electron Configurations
• Valence Electrons

Principal Quantum Numbers

• Principal Quantum Numbers:
• Show relative sizes and energy of orbital
• n = 1 (1st level)
• n = 2 (2nd level)
• n = 3 (3rd level)
• n = 4 (4th level)

Orbitals

• Orbital Shapes (s, p, d, f)
• Show arrangement of e^- in an atom
• Each orbital can hold only 2 electrons

Electron Configuration Rules

The Aufbau Principle:

• -Electron occupies the lowest energy orbital available (think 2-8-8 rule)

Write electron configuration for nitrogen. �(use Noble Gas notation)

Step 1: Identify atom on table & # of e^-

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Step 2: Write out orbitals

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Step 3: Fill in Electrons

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Step 4: Write Noble Gas config

Nitrogen

Electrons = 7

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• 1s 2s 2p

1s² 2s² 2p³

[He] 2s² 2p³

Rules for Orbital Diagrams

Pauli Exclusion Principle

• Maximum of 2 e- w/ opposite spins occupy 1 orbital
• Arrows = electrons

Hund’s Rule

• Single electrons must fill up energy levels before adding second electrons

Write orbital diagram for Oxygen.

Oxygen

Electrons = 8

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1s 2s 2p

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Step 1: Identify atom on table & # of e^-

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Step 2: Write out orbitals

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Step 3: draw arrows in each orbital for electrons

Valence Electrons

• Electrons on outer energy level (s & p)
• Shared or transferred in reactions

Lewis Dot Structures

• Show the valence electrons
• Useful to show reactions

Li

C

Al

Cl

Complete the Table