Electron Configurations & Activity 16 Intro

3 Rules to assign e - to orbitals:  Aufbau: e- occupy lowest energy orbital available  Pauli Exclusion Principle: Maximum 2 electrons per orbital Must have opposite spins  Hund’s Rule: When there are multiple orbitals at the same E (p’s, d’s, f’s, etc.) e - will fill orbitals to give max number of unpaired e- allowed Think kids on the bus!

Orbital Filling Diagrams: ENERGYENERGY 1s1s 2s2s 2p2p 3s3s 3p3p 4s4s 3d3d Manganese: 25 protons, 25 electrons Electron Configuration: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5

What we have been doing is an…  Orbital Filling Diagram Ex: Carbon (6 e - )  Can be summarized with Electron Configurations 1s 2 2s 2 2p 2  Note: e - configurations won’t show the number of unpaired electrons! E 

Electron Configurations:  Can be done without a diagram (count e - as you go)  Example:Scandium Scandium: 21 protons, 21 electrons Electron Configuration: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 1

Electron Configurations:  Can be done without a diagram (count e - as you go)  While easier, can still be LONG  So…we have even shorter short- cuts…Activity 16 will introduce them.

Noble Gas Configurations:  Use previous noble gas in square brackets to stand for the full electron configuration to that point  Example: Manganese Full configuration: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 Noble Gas Configuration: [Ar]4s 2 3d 5

Doing a Noble Gas Configuration:  Start with the previous noble gas’ symbol in square brackets  Subtract the atomic number of the noble gas from the atomic number of your element  Gives # e - left to be placed  Count down the rows to the row of your element  Place the remaining e- starting from the “row # s orbital”

Example Noble Gas Configuration: Palladium (Atomic # 46)  Previous Noble Gas: Krypton [Kr]  Subtract the atomic numbers:  46 – 36 = 10 e - remaining  Palladium is in row 5 so place the remaining 10 e- using the filling order, starting with the 5s  [Kr]5s 2 4d 8

Valence Electrons  e - that determine element’s chemical properties  Defn: e - in outermost orbitals  In other words: e - on the highest principle energy level (n)  Back to Palladium: [Kr]5s 2 4d 8  5 is highest n  Only 2 e- in the 5s are valence!

Electron Dot Diagram  Uses only the valence e -  A competing way to find the number of unpaired e -  Used for bonding (Hund’s Rule is for ATOMIC orbitals, not bonding, and may disagree with the dot diagram)

Electron Dot Diagram  Write the element’s symbol  Find number of valence electrons  Act like the symbol has 4 sides  Go around the symbol clockwise like a wheel adding 1 e - per side  Will make you put down 4 e - before pairing any e-

Example: Fluorine (Column 7A) F        # Valence Electrons: 7!

Example: Gallium  Noble Gas Config.: [Ar]4s 2 3d 10 4p 1  3 Valence electrons  e - config. says 2 paired e - in the 4s and 1 unpaired e - in the 4p  Dot Diagram: Ga    3 unpaired e - !

Practice: ENERGYENERGY 1s1s 2s2s 2p2p 3s3s 3p3p 4s4s 3d3d

Example: ENERGYENERGY 1s1s 2s2s 2p2p 3s3s 3p3p 4s4s 3d3d Fluorine: 9 protons, 9 electrons

Another way to show the order of orbital filling: