Electron Configuration
Na: 1s2 2s2 2p6 3s1
Electron Configurations
• Electron configurations tells us where the electrons in an
atom are located-similar to an address. Four
characteristics of an electron:
Energy Levels n =1, 2, 3, 4, etc.
Sublevels
s, p, d, f
s has 1 orbital, p has 3 orbitals, and
d has 5 orbitals
Orbitals can hold a maximum of 2 e’s
Spin-e’s can spin clockwise or counter-clockwise
(Electron Arrangement in Atoms handout)
Energy Level (Shell)
•distance from nucleus
•symbol, n
•aka: Principle Quantum Number (PQN)
•whole numbers between 1-7
•smaller n => closer to nucleus
•smaller n => lower energy
Sublevels (Subshells)
•subdivision within shells
•symbols, s, p, d, f
•The s sublevel has a shape of a sphere
•The p sublevel has a shape of a figure 8
•The d sublevel has a shape of a clover.
•The f sublevel has complicated shapes
Sublevels (Subshells)
•increasing energy from s to f
•EL # = number of subshells
ex.: EL#1 has 1 subshell, s
(Fill in blanks)
Orbitals
•region in space within a subshell
•contain a maximum of 2 e’s
•s has 1 orbital..can hold max of …
•p has 3 orbitals (degenerate) ..can hold..
•d has 5 orbitals (degenerate) ..can hold..
•f has 7 orbitals (degenerate) ..can hold..
Degenerate = equal in energy
Atomic Orbitals
All s orbitals are spherical in shape but differ in size:
1s < 2s < 3s
principal quantum
number (n = 2)
2s
Sublevel
Orbitals in the p Sublevel
Atomic Orbitals
The p orbitals:
Orbitals in the d Sublevel
Orbitals in the f Sublevel
2
3s
Nucleus
3pz2
2
2
2s
2pz
1s2
3px22px2
2py
2
3py2
This is a more accurate model.
Possible Locations for Electrons
Shells, subshells, and orbitals
n=1
n=2
1s __ 2s __
n=3
3s __
2p __ __ __ 3p __ __ __
n=4
4s __
4p __ __ __
3d __ __ __ __ __ 4d __ __ __ __ __
4f __ __ __ __ __ __ __
Possible Locations for Electrons
n=1
n=2
1s __ 2s __
n=3
3s __
2p __ __ __ 3p __ __ __
n=4
4s __
4p __ __ __
3d __ __ __ __ __ 4d __ __ __ __ __
4f __ __ __ __ __ __ __
Filled Energy Level # 1 = 2 e’s
Possible Locations for Electrons
n=1
n=2
1s __ 2s __
n=3
3s __
2p __ __ __ 3p __ __ __
n=4
4s __
4p __ __ __
3d __ __ __ __ __ 4d __ __ __ __ __
4f __ __ __ __ __ __ __
Filled Energy Level # 2 = 8 e’s
Possible Locations for Electrons
n=1
n=2
1s __ 2s __
n=3
3s __
2p __ __ __ 3p __ __ __
n=4
4s __
4p __ __ __
3d __ __ __ __ __ 4d __ __ __ __ __
4f __ __ __ __ __ __ __
Filled Energy Level # 3 = 18 e’s
Possible Locations for Electrons
n=1
n=2
1s __ 2s __
n=3
3s __
2p __ __ __ 3p __ __ __
n=4
4s __
4p __ __ __
3d __ __ __ __ __ 4d __ __ __ __ __
4f __ __ __ __ __ __ __
Filled Energy Level # 4 = 32 e’s
Placing electrons in the p, d, and f sublevels
2 e’s in the p sublevel:
2p2 __ __ __
NOT:
2p2 __ __ __
4 e’s in the p sublevel:
2p4 __ __ __
4 e’s in the d sublevel
3d4 __ __ __ __ __
9 e’s in the f sublevel
4f9 __ __ __ __ __ __ __
Place e’s in available
orbitals with same spin,
then pair (opposite spin)
Write this on pg. 2:
Hund’s Rule
When placing electrons in the s, p, and
d sublevel, fill the sublevel in a way
that will give the maximum number of
unpaired electrons with parallel spin.
Complete pg.2 and 3 of packet
Filling Diagram for Sublevels
Each line
represents an
orbital.
Electron Configurations
• The electron configuration of an atom is a shorthand
method of writing the location of electrons by sublevel
and energy level.
• The sublevel is written followed by a superscript with the
number of electrons in the sublevel.
– If the 2p sublevel contains 2 electrons, it is written 2p2
Electron Configurations
The electron configuration describes how the electrons are
distributed in the various atomic orbitals.
In a ground state hydrogen atom, the electron is found in the 1s
orbital.
Ground state electron
configuration of hydrogen
Energy
Energy Level
(n = 1)
2s
2p
2p
1
1s
2p
sublevel
Arrow up indicates direction of spin
1s
number of electrons in
the orbital or subshell
Electron Configurations
Pg. 1 of packet
According to the Pauli exclusion principle, an orbital can hold a
maximum of 2 electrons with opposite spins.
The ground state electron
configuration of helium
Energy
2p
2s
1s
2p
2p
1s
2
Designate spin by using an
“up” arrow and a “down”
arrow.
Electron Configurations
The Aufbau principle states that electrons are added to the lowest
energy orbitals first before moving to higher energy orbitals.
Li has a total of 3 electrons
The ground state electron
configuration of Li
Energy
2p
2s
1s
2p
2p
1s22s1
The third electron must go in the
next available orbital with the
lowest possible energy.
The 1s orbital can only accommodate 2
electrons (Pauli exclusion principle)
Electron Configurations
The Aufbau principle states that electrons are added to the lowest
energy orbitals first before moving to higher energy orbitals.
Be has a total of 4 electrons
The ground state electron
configuration of Be
Energy
2p
2s
1s
2p
2p
1s22s2
Electron Configurations
The Aufbau principle states that electrons are added to the lowest
energy orbitals first before moving to higher energy orbitals.
B has a total of 5 electrons
The ground state electron
configuration of B
Energy
2p
2s
1s
2p
2p
1s 2s 2p
2
2
1
Electron Configurations
According to Hund’s rule, the most stable arrangement of electrons
is the one in which the number of electrons with the same spin is
maximized.
C has a total of 6 electrons
The ground state electron
configuration of C
1s22s22p2
Energy
2p
2p
2p
2s
The 2p orbitals are of equal energy, or degenerate.
1s
Put 1 electron in each before pairing (Hund’s rule).
Electron Configurations
According to Hund’s rule, the most stable arrangement of electrons
is the one in which the number of electrons with the same spin is
maximized.
N has a total of 7 electrons
The ground state electron
configuration of N
1s22s22p3
Energy
2p
2p
2p
2s
The 2p orbitals are of equal energy, or degenerate.
1s
Put 1 electron in each before pairing (Hund’s rule).
Electron Configurations
According to Hund’s rule, the most stable arrangement of electrons
is the one in which the number of electrons with the same spin is
maximized.
O has a total of 8 electrons
The ground state electron
configuration of O
1s22s22p4
Energy
2p
2s
1s
2p
2p
Once all the 2p orbitals are singly occupied, additional
electrons will have to pair with those already in the
orbitals.
Electron Configurations
According to Hund’s rule, the most stable arrangement of electrons
is the one in which the number of electrons with the same spin is
maximized.
F has a total of 9 electrons
The ground state electron
configuration of F
1s22s22p5
Energy
2p
2s
1s
2p
2p
When there are one or more unpaired electrons, as
in the case of oxygen and fluorine, the atom is
called paramagnetic.
Electron Configurations
According to Hund’s rule, the most stable arrangement of electrons
is the one in which the number of electrons with the same spin is
maximized.
Ne has a total of 10 electrons
The ground state electron
configuration of Ne
1s22s22p6
Energy
2p
2s
1s
2p
2p
When all of the electrons in an atom are paired, as
in neon, it is called diamagnetic.
If keep adding e’s, the order of filling is:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p….
Two ways to determine the order of
filling:
Look at the periodic table
Use the sublevel chart
Period
No.
1s
1s
1
2s
2s
2p
2p
2p
2p
2p
2p
3s
3s
3p
3p
3p
3p
3p
3p
4s
4s
3d
3d
3d
3d
3d
3d
3d
3d
3d
3d
4p
4p
4p
4p
4p
4p
5s
5s
4d
4d
4d
4d
4d
4d
4d
4d
4d
4d
5p
5p
5p
5p
5p
5p
6s
6s
5d
5d
5d
5d
5d
5d
5d
5d
5d
5d
6p
6p
6p
6p
6p
6p
7s
7s
6d
6d
6d
6d
6d
6d
6d
4f
4f
4f
4f
4f
4f
4f
4f
4f
4f
4f
4f
4f
4f
5f
5f
5f
5f
5f
5f
5f
5f
5f
5f
5f
5f
5f
5f
2
3
4
5
6
7
6
7
Period
No.
S
1
2
3
4
S
B
L
O
C
K
P-Block
5
D-Block
6
(n-1)
7
6
F-Block
7
(n-2)
Electron Configurations: Sublevel Chart
This chart give the order
of filling.
Start at the top with 1s
and follow the arrows:
1s, 2s, 2p, etc.
Writing Electron Configurations
Write the electron configuration for calcium (#20)
Ca: 1s2 2s2 2p6 3s2 3p6 4s2
Do superscripts add to 20 ?
How many unpaired e’s?-Remember how e’s go into
sublevel orbitals?
How many valence e’s?-Determine the highest
energy level, count how many total e’s are in the
highest numbered energy level.
Writing Electron Configurations
Write the electron configuration for gallium (#31)
Ga: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1
Do superscripts add to 31 ?
How many unpaired e’s?
How many valence e’s?-BE CAREFUL!
Write the electron configuration for tin (#50)
Sn: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p2
Do superscripts add to 50 ?
How many unpaired e’s?
How many valence e’s?-BE CAREFUL!
Noble Gas Core Electron Configurations
A Shortcut !
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Neon completes the 2p subshell.
Sodium marks the beginning of a new row-3rd energy level
Na: 1s2 2s2 2p6 3s1
So, we write the condensed electron configuration for
sodium as
Na: [Ne] 3s1
[Ne] represents the electron configuration of neon.
Sodium has 1 valence electron (in a 3s orbital)
Core electrons: electrons in [Noble Gas].
Valence electrons: s and p electrons beyond the Noble Gas core.
Noble Gas Core Electron Configurations
A Shortcut !
• Recall, the electron configuration for S is:
S: 1s2 2s2 2p6 3s2 3p4
• We can abbreviate the electron configuration by indicating the
innermost electrons with the symbol of the preceding noble gas.
• The preceding noble gas with an atomic number less than sulfur is
neon, Ne. We rewrite the electron configuration:
S: [Ne] 3s2 3p4
How many valence e’s?
How many unpaired e’s?
Noble Gas Core Electron Configurations
A Shortcut !
• Write the e’-configuration for arsenic (# 33)-Use the noble gas core
shortcut:
As: [Ar]4s2 3d10 4p3
How many valence e’s?
How many unpaired e’s?
• Write the e’-configuration for zirconium (# 40)-Use the noble gas
core shortcut:
Zr: [Kr]5s2 4d2
How many valence e’s?
How many unpaired e’s?
Electron Configurations and the Periodic Table
There are several notable exceptions to the order of electron filling for some of the
transition metals.
 Chromium (Z = 24) is [Ar]4s13d5 and not [Ar]4s23d4 as expected.
 Copper (Z = 29) is [Ar]4s13d10 and not [Ar]4s23d9 as expected.
The reason for these anomalies is the slightly greater stability of d subshells that are either
half-filled (d5) or completely filled (d10).
Cr
[Ar]
4s
3d
3d
3d
3d
3d
Greater stability with half-filled
3d subshell
Electron Configurations and the Periodic Table
There are several notable exceptions to the order of electron filling for some of the
transition metals.
 Chromium (Z = 24) is [Ar]4s13d5 and not [Ar]4s23d4 as expected.
 Copper (Z = 29) is [Ar]4s13d10 and not [Ar]4s23d9 as expected.
The reason for these anomalies is the slightly greater stability of d subshells that are either
half-filled (d5) or completely filled (d10).
Cu
[Ar]
4s
3d
3d
3d
3d
3d
Greater stability with filled 3d
subshell
Honors Only
Electron configurations of Monatomic Ions
Elements at either end of a period gain or lose electrons
to attain a filled outer level. The resulting ion will have a
noble gas electron configuration and is said to be
isoelectronic with that noble gas.
Na(1s22s22p63s1) → e− + Na+([He]2s22p6)
[isoelectronic with Ne]
Br([Ar]4s23d104p5) + e− → Br- ([Ar]4s23d104p6)
[isoelectronic with Kr]
Orbital Diagrams
• Show electrons as arrows
• Show arrows in labelled sublevels
• Individual orbitals are shown as circles or
boxes
• Can use Noble-Gas Shortcut
Orbital Diagram for Oxygen
How many unpaired e’s does oxygen have?
How many valence e’s does oxygen have?
Not on the sheet
Draw a box or line even if no e’s are in it.
Give the orbital diagram for aluminum:
Give the orbital diagram for silicon and
magnesium-See board
Give the orbital diagram for rubidium.
Use the Noble-gas shortcut:
[Kr]
5s
How many unpaired e’s does rubidium have?
How many valence e’s does rubidium have?
Give the orbital diagram for lead and indium
Use the Noble-gas shortcut-See board
Excited State Electrons
• When an electron absorbs energy, it jumps to a
higher energy level (the atom is in an excited
state), then drop back down giving off energy in the
form of light and heat (the atom returns to the
ground state).
Energy
Energy in the form of light
Excited State Atoms
• The electron configuration for an excited state atom shows
one or more electrons in a higher energy level
• The electrons represented in the electron configuration are
“out of order”-They violate the Aufbau Principle.
• Excited state atom:
1s2 2s2 2p6 3s2 4s1 How do you know it’s excited?
• What element is it? How do you know?
Excited State Atoms
Element
Fluorine
Ground State
1s2 2s2 2p5
Excited State
1s2 2s22p 4 3s1
Sodium
1s2 2s2 2p6 3s1 1s2 2s2 2p6 3p1
How do you know these are excited state
atoms?
Identify as ground state or excited state
then identify the atom
1) 1s2 2s2 2p6 3s2 3p5 4s2
2) 1s2 2s2 2p6 3s2 3p6 4s2 3d4
3) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d6
1) Excited state, potassium (Z = 19)
2) Ground state, chromium (Z = 24)
3) Excited state, technetium (Z = 43)