Writing Electron Configurations
Noble gas method
Write an electron configuration for
uranium (92 electrons).
Write an electron configuration for
uranium (92 electrons).
• 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f4
Write an electron configuration for
uranium (92 electrons).
• 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f4
• This can take a long time for large atoms,
especially when the valence electrons are the
only ones we care about.
Noble gas method
• This method represents a much quicker and
easier way to identify valence electrons.
Noble gas method
• This method represents a much quicker and
easier way to identify valence electrons.
• The s-sublevel is always the first sublevel to be
filled within a particular energy level.
Noble gas method
• This method represents a much quicker and
easier way to identify valence electrons.
• The s-sublevel is always the first sublevel to be
filled within a particular energy level.
• The outermost energy level is the most
important, so why not start there?
Noble gas method
• This method represents a much quicker and
easier way to identify valence electrons.
• The s-sublevel is always the first sublevel to be
filled within a particular energy level.
• The outermost energy level is the most
important, so why not start there?
• 7s25f4 (start with the 7th energy level)
Noble gas method
• This method represents a much quicker and
easier way to identify valence electrons.
• The s-sublevel is always the first sublevel to be
filled within a particular energy level.
• The outermost energy level is the most
important, so why not start there?
• 7s25f4 (start with the 7th energy level)
• [Rn] is used to represent the first 86 electrons.
• [Rn] means the same thing as
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p6
• [Rn] means the same thing as
1s22s22p63s23p64s23d104p65s24d105p66s24f145d10
• Therefore, [Rn]7s25f4 means the same thing as
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f4
Write an electron configuration for
selenium using the noble gas
method.
Write an electron configuration for
selenium using the noble gas
method.
• Start with the s-sublevel for the period
selenium is in (4s)
Write an electron configuration for
selenium using the noble gas
method.
• Start with the s-sublevel for the period
selenium is in (4s)
• Select the noble gas from the previous period
and place it in brackets ([Ar]4s)
Write an electron configuration for
selenium using the noble gas
method.
• Start with the s-sublevel for the period
selenium is in (4s)
• Select the noble gas from the previous period
and place it in brackets ([Ar]4s)
• The argon accounts for 18 of the 34 electrons
needed. Continue until you reach 34.
Write an electron configuration for
selenium using the noble gas
method.
• Start with the s-sublevel for the period
selenium is in (4s)
• Select the noble gas from the previous period
and place it in brackets ([Ar]4s)
• The argon accounts for 18 of the 34 electrons
needed. Continue until you reach 34.
• [Ar]4s23d104p4
Electron configuration exceptions
Electron configuration exceptions
• Electrons are arranged in a way that
maximizes stability.
Electron configuration exceptions
• Electrons are arranged in a way that
maximizes stability.
• Sublevels that are filled are the most stable.
Half-filled sublevels are stable. Anything else
is unstable.
Chromium
• The noble gas configuration for chromium is
expected to be [Ar]4s23d4
Chromium
• The noble gas configuration for chromium is
expected to be [Ar]4s23d4
Chromium
• The noble gas configuration for chromium is
expected to be [Ar]4s23d4
The 3d sublevel is unstable due to the single empty
orbital.
Chromium
• The noble gas configuration for chromium is
expected to be [Ar]4s23d4
Promoting one of the 4s electrons increases stability.