ELECTRON CONFIGURATIONS The arrangement of electrons in an atom

Part I: RULES FOR E- CONFIGURATIONS 1. The Aufbau Principle Each electron occupies the lowest energy orbital available Follow the aufbau diagram for the sequence of atomic orbitals

2. Pauli Exclusion Principle Electrons are able to spin in only two directions Only two electrons may occupy a single orbital Elecrons in the same orbital must have opposite spins

3. Hund’s Rule Electrons fill empty orbitals in a sublevel first BEFORE sharing an orbital Why? Because negatively charged electrons want to be as far away from each other as possible 2p

Part II: ORBITAL DIAGRAMS Represent an atom’s electron configuration A line = each orbital Practice: Li, N, Ne 1s 2s 2p C

Part III: ELECTRON CONFIGURATIONS Superscripts = number of electrons in the orbital Add up superscripts = should equal total # of electrons in atom Practice: Ca, N, Ga

Part IV: NOBLE GAS NOTATION Electron configuration can be represented using the noble gas notation for the noble gas in the previous period and the electron configuration for the energy level being filled Practice: P, Ca, Sr