Electron Arrangement in Atoms

 Electron configurations  Aufbau principle  Pauli exclusion principle  Hund’s rule

 ELECTRON CONFIGURATIONS: Series of sublevel notations which describes what sublevels electrons currently reside in  Tells you where the electrons are  3 Rules to electron configuration Aufbau’s Principle Pauli Exclusion Principle Hund’s Rule

 Electrons occupy orbitals of lowest energy first  Each box represents an orbital Aufbau Diagram

 Range of an energy level can overlap those of another  Think crossing your fingers

 No more than two electrons in an orbital and they must have opposite spin Spin can be thought of as clockwise and counterclockwise Vertical arrows up or down indicate direction of spin

 Must be one e - in each orbital of equal energy before pairing  Remaining spot filled with e - of opposite spin

 To write electron configs for an element: Determine # of electrons the element has  The atomic number tells you how many e - if the element is neutral, which we will assume is the case Fill sublevels of lowest energy first  Use Aufbau diagram (left side) to figure out who is lowest  Put electrons in orbital until filled For every electron in a sublevel, indicate with the sublevel name and a superscript  Example: He = 2 e -, written as 1s 2  C = 6 e -, written as 1s 2 2s 2 2p 2

 To figure out which sublevels filled first: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f

 Write the electron configurations for the following elements  B  Cl  P  Ar  Ca  Ti  Fe  Hg  Er

Aufbau Diagrams