# Modern_Atomic_Theory

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Modern Atomic Theory
Quantum Numbers
Quantum Numbers
Quantum Numbers
Rules
 The Aufbau principle states that energy
levels must be filled from the lowest to the
highest and you may not move on to the
next level unless the previous level is
full. Use the periodic table as a guide
Rules
 Hund’s Rule says that when placing
electrons in orbitals of equal energy, place
one in each orbital before doubling up in
order to arrive at the lowest energy
configuration.
 The Pauli Exclusion Principle states that
when electrons do share an orbital, they
must be of different “spin.”
Rules
 Exceptions to the rules
There are a few exceptions to the rules
listed above when filling electron
configurations. A half-full “s” orbital and a
“d” subshell with 5 or 10 is more stable
than following the Aufbau Principle. Cr,
Mo, W: s1 d5 and Cu, Ag, Au: s1 d10
Electron Configurations
 Orbital information is often described in a
shorthand notation called an electron
configuration

1s22s22p3
Electron Configurations

Represents the                 Shows the number of
principal energy level         electrons in the orbital

1s2

Indicates the shape of
the orbital
Orbital Diagrams
 This information is also described using
orbital diagrams. Arrows are added to an
orbital diagram to show the distribution of
electrons in the possible orbitals and the
relative spin of each electron

__      __       __ __ __
1s        2s             2p
Writing Electron Configurations
 Determine the number of electrons in the atom
from its atomic number
 Add electrons to the sublevels in correct order of
filling
 s = 2, p = 6, d = 10, f =14
 To check your complete electron configuration,
look to see whether the location of the last
electron added corresponds to the element’s
position on the periodic table
Drawing Orbital Diagrams
 Draw a line for each orbital of each sublevel
mentioned in the complete electron
configuration.
 Draw one line for each s sublevel, three for each
p sublevel, 5 for each d sublevel and 7 for each f
sublevel.
 Label each sublevel
 For orbitals containing two electrons, draw one
arrow up and one arrow down to indicate the
electrons’ opposite spins.

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