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.