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Unformatted text preview: -13 1. The statement that “the lowest energy configuration for an atom
is the one having the maximum number of unpaired electrons
allowed by the Pauli principle in a particular set of degenerate
orbitals” is known as:
a. The Aufbau principle
b. Hund’s Rule
c. Heisenberg Uncertainty Principle
d. The Pauli Exclusion Principle.
d. Which of the following electron configurations is not possible?
1s2 2s2 2p3
1s2 2s2 2p6
1s2 2s2 2p6 2d2
1s2 2s2 2p6 3s1 Example. What are the electron configurations for the following
Ni Electron configurations and noble gases
Writing out electron configurations can be long and tedious.
However, there are shortcuts.
Consider the following:
Ne 1s2 2s2 2p6
Mg 1s2 2s2 2p6 3s2 [Ne] ___________ Ar 1s2 2s2 2p6 3s2 3p6
K 1s2 2s2 2p6 3s2 3p6 4s1 [Ar] 4s1 10 05-Sep-13 Exceptions to the Aufbau principle
For Cr we expect the electron configuration to be [Ar]4s23d4.
Experimentally we see [Ar]4s13d5. Why?
3d ____ 4s ____ 3p ____ 3s ____ 2p ____ 2s ____ 1s ____ ____ ____ ____ ____ ____ ____ ____ The reason for this exception is
not completely understood, but
it seems that a half-filled 3d
subshell (for Cr) lends a special
stability to the observed
electron configuration. ____
Similar exceptions are
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