SECTION 3:
ELECTRON
CONFIGURATIONS
CHAPTER 9: ELECTRONS IN ATOMS
AND THE PERIODIC TABLE
Learning Goals
•Apply the Pauli exclusion
principle, the aufbau principle,
and Hund's rule to write electron
configurations using orbital
diagrams and electron
configuration notation.
Electron Configuration
• An electron configuration
shows how the electrons occupy
the orbitals for a particular atom.
• The aufbau principle states
that each electron occupies the
lowest energy orbital available.
1s orbital
2 electrons
2s orbital
2 electrons
2p orbital
6 electrons
3s orbital
2 electrons
3p orbital
6 electrons
4s orbital
2 electrons
3d orbital
10 electrons
4p orbital
6 electrons
5s orbital
2 electrons
4d orbital
10 electrons
5p orbital
6 electrons
6s orbital
2 electrons
4f orbital
14 electrons
5d orbital
10 electrons
6p orbital
6 electrons
7s orbital
2 electrons
5f orbital
14 electrons
6d orbital
10 electrons
7p orbital
6 electrons
Electron Configuration
• Hund’s rule states that single
electrons must occupy each equalenergy orbital before additional
electrons with can occupy the
same energy level orbitals.
• All electrons in singly occupied
orbitals must have the same spin.
• School bus rule
Electron Configuration
• The Pauli exclusion principle
states that a maximum of two
electrons can occupy a single
orbital, but only if the electrons
have opposite spins.
• We symbolize this as two arrows
pointing in opposite directions.
Orbital Notation Examples
• Write the orbital notation electron configuration for
the following atoms or ions. State how many
unpaired electrons are in each.
a. N
b. Cl
Orbital Notation Examples
c. Al
d. V
Orbital Notation Examples
e. Li+
f. O2-
Electron Configuration
• Electron Configurations Using
the Periodic Table:
• Read the periodic table from left to
right to determine the electron
configuration.
Electron Configuration
• Write the ground state electron
configuration for the following:
a. C
b. Fe
Electron Configuration
c. W
d. S2-
Electron Configuration
• Noble gas notation uses noble gas
symbols in brackets to shorten
inner electron configurations of
other elements.
• The noble gas must have a lower
atomic number than the atom or ion
that the electron configuration is
being written for.
Noble Gas Notation
a. W
b. Eu
Noble Gas Notation
c. As
d. O
Electron Configuration
• The aufbau diagram can be used to
write correct ground-state electron
configurations for all elements up to
and including Vanadium, atomic
number 23.
• The electron configurations for certain
transition metals, like chromium and
copper, do not follow the aufbau
diagram due to increased stability of
half-filled and filled sets of s and d
orbitals.
Electron Configuration
• Chromium:
1
5
[Ar]4s 3d
• Copper: [Ar]4s13d10
• These exceptions occur
because a half-filled d subshell
and a completely filled d
subshell are particularly stable
Electron Configuration
•The number of outer-shell
electrons in a transition series
does not change as you move
across a period.
• The transition series represents
the filling of core orbitals and the
number of outershell electrons is
mostly constant—either 2 or 1.
Electron Configuration
(2e–) for 4s23dx
(1e–) for
1
5
4s 3d or
1
10
4s 3d