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

Electron Spin One electron spins clockwise, the other counter-clockwise.

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

Write the e- configuration for lead. Aufbau Diagram Write the e- configuration for lead.

Hund’s Rule 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.

Reading Electron Configurations from the Periodic Table

Condensed Electron Configurations Ne completes the 2p subshell. Na marks the beginning of a new row. So, we write the condensed electron configuration for Na as Na: [Ne] 3s1 [Ne] represents the electron configuration of neon.

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

Unusual Electron Configurations 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

Anomalous Electron Configurations Anomalous = unusual Know Cr, Mo, Cu, and Ag! Element Actual Expected Cr [Ar]3d54s1 [Ar]3d44s2 Cu [Ar]3d104s1 [Ar]3d94s2 Ag [Kr]4d105s1 [Kr]4d95s2