Section 4-3 Electron Configurations

Quantum Mechanical Model Energy Levels have sublevels Each sublevel contains orbitals –Orbital – a 3-D region around the nucleus that indicates the probable location of an electron Every orbital can hold 2 electrons

Types of Sublevels S Sublevel – 1 orbital –Sphere shaped –Holds 2 electrons P Sublevel – 3 orbitals –Dumbbell shaped –Holds 6 electrons D Sublevel – 5 orbitals –Holds 10 electrons F sublevel – 7 orbitals –Holds 14 electrons

Orbital Shapes

Energy Level Sublevels# of orbitals # electrons/ orbital 1s12 2sPsP sPdsPd spdfspdf

Electron Configurations Arrangement of electrons in an atom –Distinct for each element because they all have different numbers of electrons. –Electrons assume arrangements that have the lowest possible energies

Aufbau Principle Electrons are added one at a time to the lowest energy orbital until all the electrons have been accounted for. –Ex: the 4s sublevel gets filled before the 3d sublevel

Pauli Exclusion Principle An orbital can hold a maximum of two electrons. To occupy the same orbital, the 2 electrons must spin in opposite directions.

Hund’s Rule The electrons fill up all the orbitals of the sublevel with parallel spins before they begin to pair up.

Electron Configurations Al – 1s 2 2s 2 2p 6 3s 2 3p 1 S – 1s 2 2s 2 2p 6 3s 2 3p 4