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Electron Configurations & Activity 16 Intro
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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!
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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
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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
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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
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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.
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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
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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”
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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
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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!
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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)
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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-
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Example: Fluorine (Column 7A) F # Valence Electrons: 7!
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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 - !
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Practice: ENERGYENERGY 1s1s 2s2s 2p2p 3s3s 3p3p 4s4s 3d3d
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Example: ENERGYENERGY 1s1s 2s2s 2p2p 3s3s 3p3p 4s4s 3d3d Fluorine: 9 protons, 9 electrons
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Another way to show the order of orbital filling:
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