013-Aufbau Principle, Hund's Rule and Electron Configuration
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Transcript of 013-Aufbau Principle, Hund's Rule and Electron Configuration
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7/26/2019 013-Aufbau Principle, Hund's Rule and Electron Configuration
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Aufbau Principle
Electrons fill orbitals starting at the lowest
available (possible) energy states beforefilling higher states (e.g. 1sbefore 2s).
(Instead of p85, 1)
Lower-energy orbitals fill before higher-energy orbitals.
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Orbital Diagram for Hydrogen
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Orbital Diagram for Helium
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Orbital Diagrams for Lithium and Beryllium
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Orbital Diagram for Boron
All the 2p orbitals are degenerate, it does not
matter which 2p orbital the electron occupies.
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Orbital Diagram for Carbon
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Hunds Rule
The lowest energy configuration for an atom
is the one having the maximum number ofunpaired electrons allowed by the Pauli
principle in a particular set of degenerate
orbitals. (p85, r2)
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Hunds Rule
If two or more orbitals with the same energy
are available, one electron goes into eachuntil all are half-full. The electrons in the
half-filled orbitals all have the same spin.
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Electron Configuration for Carbon
The configuration for carbon could be written
1s2
2s2
2pl
2pl
(more exactly, 1s2
2s2
2px1
2py1
)to indicate that the electrons occupy separate
2p orbitals. (p85, r1)
However, the configuration is usually givenas 1s
22s
22p
2, and it is understood that the
electrons are in different 2p orbitals. (pp85-86)
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Orbital Diagrams for N, O, F, Ne
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Abbreviated Configurations
To avoid writing the inner-level electrons. (p86, r4)
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Outermost Electron Configurationsfor the First 18 Elements
p86, Figure 2.27
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Orbitals Being Filled for Elementsin Various Parts of the Periodic Table
p88, Figure 2.29
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Orbital Filling
ArK, CaSc, Ti , V,
3p 4s3d
The (n + l)s orbitals always fill before the nd
orbitals. (p88, 3)
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The Order of Orbital Filling
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Lanthanides and Actinides
XeCs, BaLa, Ce , (Hf )
5p 6s4f(5d)
These series of elements corresponds to the
filling of the seven 4f (5f) orbitals. (pp88-89)
Note that sometimes an electron occupies a
5d(6d) orbital instead of a 4f (5f) orbital.
This occurs because the energies of the 4f (5f)
and 5d(6d) orbitals are very similar.