Electron Arrangement in Atoms. Electron configurations Aufbau principle Pauli exclusion principle Hund’s rule.

ChemistryElectron

Arrangement in Atoms

Section 2 Terms Electron configurations Aufbau principle Pauli exclusion principle Hund’s rule

Go (con)Figure 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

Aufbau’s Principle 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

The Pauli Exclusion Principle

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

Hund’s Rule Must be one e- in

each orbital of equal energy before pairing

Remaining spot filled with e- of opposite spin

Writing Electron Configs

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 1s2

C = 6 e-, written as 1s2 2s2 2p2

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

Section 2 Assignment Write the electron configurations for the

following elements B Cl P Ar Ca Ti Fe Hg Er

Aufbau Diagram

Aufbau Diagrams

Aufbau Diagrams