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ChemistryElectron
Arrangement in Atoms
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Section 2 Terms Electron configurations Aufbau principle Pauli exclusion principle Hund’s rule
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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
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Aufbau’s Principle Electrons
occupy orbitals of lowest energy first
Each box represents an orbital
Aufbau Diagram
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Range of an energy level can overlap those of another
Think crossing your fingers
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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
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Hund’s Rule Must be one e- in
each orbital of equal energy before pairing
Remaining spot filled with e- of opposite spin
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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
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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
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Section 2 Assignment Write the electron configurations for the
following elements B Cl P Ar Ca Ti Fe Hg Er
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Aufbau Diagram
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Aufbau Diagrams
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Aufbau Diagrams