Electron Configuration

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Electron Configuration
Energy Levels the energy levels of electrons
within an atom are represented by quantum
numbers

• Principal Quantum Number (n) represents
• the principal energy level. n is equal to
• the number of the principal energy level as
• referred to under the Bohr atom and is the
• same as the period number in the periodic
• table.

Ex Magnesiums (Mg) Principal Quantum Number
is 3 because it is in the 3rd period. This
means that that element has three energy levels
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• Sublevels principal energy levels may be
• divided into sublevels

• The total number of sublevels for each
• principal energy level is equal to the
• number of the principal energy level.

Ex The first principal energy level has one
sublevel. The second principal energy level has
two sublevels
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The sublevels and what they look like
The s sublevel The first energy level has one
sublevel called the s sublevel. It has one
orbital.
The p sublevel The second energy level has
two sublevels called the s and the p sublevels.
This sublevel has four orbitals.
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The d sublevel The third energy level has three
sublevels called the s p and d sublevels.
Nine orbitals
The f sublevel The fourth energy level and
beyond have four sublevels called the s p d
and f sublevels. Sixteen orbitals.
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• Orbitals each sublevel may consist of one or
• more orbitals with each orbital having a
• different spatial orientation

- Each electrons occupies an orbital
- An orbital can hold no more than two electrons
- The number of orbitals within the same
principal energy level (n) is equal to n2
when n is less than or equal to four
Ex the first principal energy level has only
one orbital (the s orbital) 12 1
the second principal energy level has
four orbitals (the one s orbital and the three
p orbitals) 22 4
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This might seem very confusing but try to think
of electron configuration as dwellings and the
electrons as people living in these dwellings
Each principal energy level can hold a certain
amount of electrons. The first can hold two
so it would be like a small one bedroom house.
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- The second principal energy level can hold up
to ten electrons so it would be like a large
house. It would fill the first bedroom (the 1s
sublevel) with two people (electrons) then the
second room (2s sublevel) with two people
(electrons) next would be the kids rooms (the
2p sublevels). Each kid (electron) would want
their own room (one of the 2p orbitals. When
the fourth kid comes along they would have to
start sharing rooms until each room has two
kids (electrons).
2p
1s
2s
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Writing Electron Configurations
Electron configuration of the atoms in order of
their atomic numbers starting with hydrogen can
be build up by adding one electron at a time
according to the following rules
1. No more than two electrons can be
accommodated in any orbital. (the two electrons
in the same orbital have an opposite spin)
2. The added electron is place in the unfilled
orbital of lowest energy.

• In a given sublevel a second electron is not
  added to
• an orbital until each orbital in the sublevel
  contains
• one electron

4. No more than four orbitals are occupied in
the outermost principal energy level of any
atom.
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In an electron configuration the number of
electron in a sublevel is indicated by a
superscript following the designation of the
sublevel.
Electrons will fill in the orbitals of lowest
energy possible. They will always fill the
orbitals in this order
Ex Calcuim would be represented as 1s2 2s2
2p6 3s2 3p6 4s2 or Ar 4s2 in kernel notation
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Ground State When electrons fill the orbitals
of lowest energy possible they are said to be in
the ground state
- When electrons are given some energy they
do not fill the orbitals from lowest energy up.
This is called the excited state.
Valance Electrons The electrons in the
outermost principal energy level of an atom.
- The chemical properties of an atom are
related to the valence electrons.
- The term kernel is used to refer to the
atom exclusive of the valence electrons. The
kernel consists of the nucleus and all the
electrons except the valence electrons.
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Ionization Energy The amount of energy required
to remove the most loosely bound electron from
an atom in the gaseous phase.
- Ionization energy refers to the removal of the
first electron.
- The second ionization energy refers to the
removal of the second most loosely
bound electron.
- Each successive ionization energy is
greater than the previous one.
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