Section: 3.3 - Electron Configurations and Periodic Trends • Electron Configuration – a shorthand notation that shows: – The number of electrons – The arrangement of electrons in orbitals • An atom’s ground state electron configuration determines most chemical properties • Therefore we usually write electron configurations for atoms in ground state
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Section: 3.3 - Electron Configurations and Periodic Trends Electron Configuration – a shorthand notation that shows: – The number of electrons – The arrangement.
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Section: 3.3 - Electron Configurations and Periodic Trends
• Electron Configuration – a shorthand notation that shows:– The number of electrons– The arrangement of electrons in orbitals
• An atom’s ground state electron configuration determines most chemical properties
• Therefore we usually write electron configurations for atoms in ground state
Fig. 3.19 - Atomic Orbitals and Relative Energies
Writing Electron Configurations• Using Boron as an example
# of electrons in each sublevel
1s22s22p1
Letters represent orbital shape
Principal Quantum Number (Energy Level)
We do not need spin numbers...they must be opposite if they are in the same sublevel
Orbital Diagrams/Energy Level Diagrams
• Use boxes or circles to represent each orbital= empty orbital= orbital with one electron (+1/2 spin)= orbital with one electron (-1/2 spin)= orbital with 2 electrons...with opposite
spin
Completing Orbital Diagrams and Writing Electron Configurations
• For Lithium1s22s1
1s 2s• For Nitrogen
1s22s2p3
1s 2s 2p • For Oxygen
1s22s23p4
1s 2s 2p* The text uses circles and places orbitals vertically from lowest to highest
Condensed Electron Configurations• For atoms with a large number of electrons• The configuration is very large• For Potassium (Atomic # = 19)
1s22s22p63s23p64s1
• Condensed Form - Element symbol for previous Noble Gas represents the orbitals up to that point. Additional orbitals are added to it.
• For Potassium – previous Noble Gas is argonCondensed Electron Configuraton
[Ar]4s1
Electron Configurations for Period 4
• Notice that the 4s orbital has a lower energy level than 3d orbitals
• Therefore 4s fills before 3d (Aufbau Principle)
K [Ar]4s1
Ca [Ar]4s2
Sc [Ar]4s23d1
Ti [Ar]4s23d2
Fig. 3.19 - Atomic Orbitals and Relative Energies
Exceptions to the Aufbau Principle• Some elements are more stable when they do
not follow the Aufbau Principle• Eg. Cr is most stable when it have only 1
electron in 4s and 1 in each of the 3d orbitalsie.
4s 3d
4s 3d
Patterns in Electron Configuration and Periodic Table Location
Patterns in Electron Configuration and Periodic Table Location
• For Main Group Elements – last number in the group number = # of valance electrons
Eg. O is group # 16 – has 6 valance electrons
• The n value of the highest occupied energy level is the period number
Eg. For Li – 1s22s1
Li is in period 2 For K – [Ar]4s1
K is in period 4
Patterns in Electron Configuration and Periodic Table Location
• n2 = the total number of orbitals in that energy level
For n = 2, there are n2 = 4 orbitals (one 2s orbital and three 2p orbitals)
• 2n2 = the maximum number of electrons in an energy level
For n = 2, there are 2n2 = 8 electrons max
Examining the Periodic Table
• Elements with similar properties in the periodic table are filling the same subshell
• Look at the electron configuration for lead– What does it look like?– How does the electron configuration explain why this
transition metal can form both Pb2+ and Pb4+ ions?
• Magnetism– Look at configuration for iron. What do you notice