Electron Configurations Objectives: Determine the electron configurations of elements using the principles of orbital energy, orbital capacity & electron spin.

4-5 Electron Configurations This refers to the distribution of electrons among orbitals of an atom. This refers to the distribution of electrons among orbitals of an atom. It is determined by distributing electrons among levels, sublevels and orbitals according to these rules: It is determined by distributing electrons among levels, sublevels and orbitals according to these rules: Aufbau Principle Aufbau Principle Pauli Exclusion Principle Pauli Exclusion Principle Hund’s Rule Hund’s Rule Orbital diagrams are used to write the electron configurations. Orbital diagrams are used to write the electron configurations.

The Rules for Electron Configurations Aufbau Principle: Electrons are added one at a time to the lowest energy orbitals until all electrons have been included. “Lazy Tenant Rule”

Rules (cont’d): Pauli Exclusion Principle Each orbital can hold only TWO electrons with opposite spins. Each orbital can hold only TWO electrons with opposite spins.

RIGHT WRONG Rules (cont’d) Hund’s Rule Within a sublevel, place one e - per orbital before pairing them. Within a sublevel, place one e - per orbital before pairing them. “Empty Bus Seat Rule” “Empty Bus Seat Rule”

Orbital Filling Order This pneumonic shows how the complex orbitals of large atoms overlap and fill “out of order.”

Electron configuration demonstrations WorkshopFolder/Electroncon fnew.html WorkshopFolder/Electroncon fnew.html WorkshopFolder/Electroncon fnew.html WorkshopFolder/Electroncon fnew.html

H 1e - Electron Configuration Electron Configuration 1s 1 Orbital Diagrams 1s 2s 2p

Orbital Diagrams

Your turn….. Your turn….. Practice on worksheet Practice on worksheet

Writing Electron Configurations H1s 1 He 1s 2 Li 1s 2 2s 1 C1s 2 2s 2 2p 2 S1s 2 2s 2 2p 6 3s 2 3p 4

Exceptions to the Aufbau Principle Recall that some orbitals are very close in energy. Recall that some orbitals are very close in energy. This is especially true for large atoms having lots of d and f orbitals. This is especially true for large atoms having lots of d and f orbitals. This causes certain orbitals to fill before one would normally expect. This causes certain orbitals to fill before one would normally expect. Chromium and Copper illustrate the exceptions (page 153). Chromium and Copper illustrate the exceptions (page 153). A certain amount of energy stability results from half-filled orbitals, and this accounts for the orbital filling order in Cr and Cu. A certain amount of energy stability results from half-filled orbitals, and this accounts for the orbital filling order in Cr and Cu.

Exceptions Chromium Instead of: Instead of: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 5Copper Instead of: Instead of: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 9 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10

Did we meet the OBJECTIVES? Describe a wave in terms of its frequency, wavelength, speed & amplitude. Identify the regions of the electromagnetic spectrum. Relate energy of radiation to its frequency. Explain what is meant by a “quantum of energy.” Distinguish between a ‘continuous’ spectrum & a ‘line’ spectrum. State the main idea in Bohr’s model of the hydrogen atom. Describe atomic orbitals in terms of shape, size & energy. Determine the electron configurations of elements using the principles of orbital energy, orbital capacity & electron spin.

WOW! We sure covered a lot of territory! You have finished a very difficult, but important, chapter in Chemistry. CONGRATULATIONS!