Orbitals and Their Energies

• Orbital energy increases in this order: s< p < d < f• Degenerate orbitals: all

orbitals in the same subshell. All have same energy.• Example: p-orbitals are

degenerate

Electron Configurations

• Tells which orbitals are assigned for each electron in an atom. • There are three rules to guide

configurations.• Pauli Exclusion Principle• Aufbau Diagram• Hund’s Rule

Pauli’s Exclusion Principle

• At most, there can be two electrons in a given orbital and they must have opposite spin.• One spins clockwise, the other

counter-clockwise. • In block diagrams, we show this

as: = clockwise; = counterclockwise

One electron spins clockwise, the other counter-clockwise.

Electron Spin Electron Spin

• Aufbau Diagram: electrons fill orbitals from lower energy to higher energy.

• Electrons do NOT always fill all orbitals in same energy level before starting to fill the next level!

Aufbau DiagramAufbau Diagram

1. Use the Aufbau Diagram to write the e- configuration for nitrogen.

2. Use the Aufbau Diagram to write the e- configuration for iron.

Aufbau DiagramAufbau Diagram

Write the e- configuration for lead.

Aufbau DiagramAufbau Diagram

• Hund’s Rule: For degenerate orbitals, need to maximize the number of electrons with same spin.

• Fill each degenerate orbital with a single electron spinning in one direction before adding each orbital’s second electron spinning in the opposite direction.

Hund’s RuleHund’s Rule

Reading Electron Configurations from the Periodic Table

• Ne completes the 2p subshell.• Na marks the beginning of a new row.• So, we write the condensed electron

configuration for Na asNa: [Ne] 3s1

• [Ne] represents the electron configuration of neon.

Condensed Electron Condensed Electron ConfigurationsConfigurations

Core and Valence Electrons

• Core e-’s: electrons in closed shells. Usually in [brackets] in condensed e-configs.• Valence electrons: Electrons in the

highest principal quantum level and unfilled lower quantum levels of an atom. • [Ar]3d84s2 [Core] Valence• [Ar]3d104s24p1 [Core] Valence

• Lanthanides & Actinides = rare earth elements

• 4f and 5f block• First three lanthanides and actinides

have unusual electron configurations.• La: [Xe]6s25d1 Ce: [Xe]6s25d14f1 Pr:

[Xe]6s24f3

Unusual Electron ConfigurationsUnusual Electron Configurations

Anomalous Electron Configurations

Element Actual Expected

Cr [Ar]3d54s1 [Ar]3d44s2

Cu [Ar]3d104s1 [Ar]3d94s2

Ag [Kr]4d105s1 [Kr]4d95s2

• Anomalous = unusual• Know Cr, Mo, Cu, and Ag!