How are electrons distributed in an atom?

Electron ConfigurationElectron Configuration  Shorthand method for representing electrons’ distribution in orbitals within subshells  All orbitals have the same energy level— digenerate  Orbitals – mathematical expressions of probability of electron’s location  Electrons occupy orbitals in a way that gives LOWEST energy state

Aufbau PrincipleAufbau Principle  Electrons occupy the LOWEST energy orbital available  Lazy Hogs !

Hund’s RulesHund’s Rules  Developed by Friedrich Hund  Creates the most stable electron arrangement  Based on electron spin

Hund’s Rules cont.Hund’s Rules cont. 1)One electron MUST occupy each orbital BEFORE electrons are paired in the same orbital. 2)Electrons added to subshell with the same spin (+1/2, -1/2) so each orbital has one electron.

Pauli Exclusion PrinciplePauli Exclusion Principle  Only 2 electrons occupy each orbital  Electron spins MUST be opposite/paired when 2 electrons occupy the same orbital  +1/2, -1/2 

Using the periodic table--Using the periodic table--  Period numbers = principal quantum number of valence shell electrons  Subshells fill with electrons at different regions within periodic table (s section, p section)

Ex. 1 NitrogenEx. 1 Nitrogen

Ex. 2 CrEx. 2 Cr

Orbital DiagramsOrbital Diagrams  Visual representation of electron configuration  Represents electrons’ spins ( ,  )

Ex. 3 MgEx. 3 Mg

Ex. 4 SnEx. 4 Sn

Practice 1)Boron6) Mn 2)Copper7) O 3)Sodium8) Li 4)Ca 5) Br