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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.