Electron Configuration
Chemistry
Learning Objectives
• TLW express the arrangement of electrons
in atoms through electron configurations
(TEKS 6.E)
Agenda
•
•
•
•
•
Electron Configuration Overview
Aufbau Principle and Diagram
Pauli Exclusion Principle
Hund’s Rule
Writing Electron Configurations
– Full, Noble Gas, For Ions
• Orbital (Box) Diagrams
• Exceptions
• Group and Individual Practice
Electron Configurations
The way electrons are arranged in atoms:
1. Every element has a specific electron
configuration – NO two are alike
2. Very important = scientists know how
an atom will react and how to manipulate
that element
Break into Lab Teams – each with an Atom
Building Game as we Inquire about econfig
Take your Periodic Table to add info
Three Rules for Electron
Configuration
• Aufbau Principle
• Pauli Exclusion Principle
• Hund’s Rule
1. Aufbau Principle
a. Electrons enter the lowest
energy level first
b. Orbitals do overlap – so
Aufbau’s principle plays a
very important part in writing
electron configuration
c. so, 1s
would
fill first;
followed
by 2s,
then 2p
etc
Aufbau’s
principle
2. Pauli Exclusion Principle
a. at most there is only 2 electrons
per orbital
b. Different spin for each
c. there are four orbitals =s, p, d, f
1s
2s
2p
3. Hund’s Rule
a. electrons do not pair up until
they have to
b. the empty bus seat
Wrong
Right
C. Writing electron configuration
1. Remember the 3 rules:
Aufbau’s, Pauli’s and Hund
2. Orbitals DO NOT fill in a nice
neat order; orbitals overlap
3. Must fill lowest energy FIRST
(Aufbau’s)
st
nd
4. 1 energy level is s; 2 is s & p;
3rd is s, p & d; 4th is s, p, d & f
5. This is the order electrons fill up
in going from lowest to highest
energy level per Aufbau Principle
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p
6s 4f 5d 6p 7s 5f 6d 7p 6f 7d 7f
6. Orbital Diagram (Box Diagrams)
Oxygen
8 e1s
2s
2p
• Electron Configuration
2
2
4
1s 2s 2p
D. Practice
Let’s determine the electron
configuration for Phosphorus
A total of 15 electrons
Increasing energy
7s
6s
5s
7p
6p
5p
4p
4s
6d
5d
4d
3d
3p
3s
2p
2s
1s
Aufbau diagram
5f
4f
7p
7s
Increasing energy
6s
5s
6p
5p
4p
4s
6d
5d
4d
5f
4f
3d
3p
3s
2s
1s
•
The
first
two
electrons
2p
go into the 1s orbital
• Notice the opposite
spins
• only 13 more to go...
7p
7s
Increasing energy
6s
5s
6p
5p
4p
4s
6d
5d
4d
3d
3p
3s
2s
1s
• The next 2
2p
electrons go into
the 2s orbital
• only 11 more...
5f
4f
7p
7s
Increasing energy
6s
5s
6p
5p
4p
4s
6d
5d
4d
3d
3p
3s
2p
2s
1s
• The next 6
electrons go into
the 2p orbital
• only 5 more...
5f
4f
7p
7s
Increasing energy
6s
5s
6p
5p
4p
4s
6d
5d
4d
3d
3p
3s
2p
2s
1s
• The next 2
electrons go into
the 3s orbital
• only 3 more...
5f
4f
7p
7s
Increasing energy
6s
5s
4s
3s
2s
1s
6p
5p
4p
6d
5d
4d
5f
4f
3d
3p • The last three electrons
go into the 3p orbitals.
2p • They each go into
separate shapes
• 3 unpaired electrons
• = 1s22s22p63s23p3
The easy way to remember
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
1s
• 2 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
1s 2s
• 4 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
• 12 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
6
2
1s 2s 2p 3s 3p 4s
• 20 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2
• 38 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2 4d10 5p6 6s2
• 56 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
• 88 electrons
Aufbau Principle
Fill from the bottom up (lowest energy
levels) first following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
5f14 6d10 7p6
• 108 electrons
Practice Again
S 16e2
1s
2s2 2p6 3s2 3p4
Core Electrons
Valence Electrons 6
Practice one more time
Cl 17 e1s2
2s2 2p6
2
3s at this point we need 5 more
3p5
So Cl is 1s22s22p63s23p5
with 7 valence electrons
Shorthand Writing e- Configs
• Noble Gas Notation
• Noble Gas Notation:
C = [He]2s22p2
Br = ?
Group Practice
• Using the Build-an-Atom Game determine the
electron configurations for the 36 elements in Lab C1, Section 4 Table
E. Exceptions to the rules
1. Orbitals fill in order
2. Lowest energy to highest
energy
3. Adding electrons can change
the energy of an orbital
4. Half filled orbitals have a lower
energy
5. Half filled orbitals make an atom
more stable
6. this stability can change the order
in which electrons fill up an
orbital
7. so if you have 4s2 and 3d9
it is better to have 4s1 and 3d10
8. Because a full or half is more stable
than a 7, 8, 9
9. BUT only in certain elements
10. Example
Titanium - 22 electrons =
2
2
6
2
6
2
2
1s 2s 2p 3s 3p 4s 3d
Vanadium - 23 electrons =
1s22s22p63s23p64s23d3
Chromium - 24 electrons =
1s22s22p63s23p64s23d4
But this is wrong for chromium!!
We expect chromium to be
1s22s22p63s23p64s23d4
BUT it is really:
1s22s22p63s23p64s13d5
Why?
This gives two half orbitals
Which means more stable atom
And slightly lower energy
11. Another Exception Copper
Copper has 29 electrons so we
expect: 1s22s22p63s23p64s23d9
But the actual configuration is:
1s22s22p63s23p64s13d10
This gives one filled orbital and
one half filled orbital.
Remember these exceptions:
4
9
d ,d
12. Writing e- Configs for Ions
• For anions – add arrows to boxes and add
to orbitals to written format
– Example – O21s2 2s2 2p6
1s
2s
2p
• For cations – remove arrows from boxes
and subtract from orbitals in written format
– Example – Li1+
– 1s2 2s1
Group Practice
1. What is the electron configuration
7s 7p 7d 7f
for Strontium?
6s 6p 6d 6f
Sr has 38 electrons
5s 5p 5d 5f
1s2
2s2 2p6 3s2 3p6 4s2
3d10 4p6 5s2
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
Electron configuration is
2
2
6
2
6
2
10
6
2
1s 2s 2p 3s 3p 4s 3d 4p 5s
Increasing energy
2. What is the electron configuration
of Cadmium?
1s 2s2 2p6 3s2 3p6
2 2
Cd has 48 electrons 4s 3d10 4p6 5s2
7s
6s
5s
7p
6p
2
6
2 4s
6
2 3s
6
2 2s
2
1s
5p
4p
3p
6d
5d
10
4d
10
3d
5f
At this point
we have 38
4f
Need 10 more
4d10
2p
22s22p
63s-2page
diagram
367 23d104p65s24d10
1sAufbau
3p64s
3. What element has an electron
configuration of:
1s22s22p63s23p64s23d104p65s24d105p3
Answer: 2+2+6+2+6+2+10+6+2+10+3
The element with 51 electrons
Antimony
4. Determine electron configuration
of Oxygen?
8 electrons
1s2
2s2
4
2p
2
2
4
Answer: 1s 2s 2p
5. How many valence electrons
does oxygen have?
if the electron configuration is
1s22s22p4
then is has 6 valence electrons
Electron Configuration
Shorthand
• You can write an element’s electron
configuration beginning with the closest
Nobel Gas
• For example – Rather than write Strontium
as 1s22s22p63s23p64s23d104p65s2 you
could just write [Kr]5s2
Summary
1. Fill lower energy levels 1st (Aufbau Principle)
2. Remember 2 electrons per orbit (Pauli Exclusion Principle)
3. Electrons don’t pair up until they must - Fill “up” arrows 1st (Hund’s Rule)
4. Energy Levels = Periods = Rows
1st energy level has an s orbital
2nd has s and p = 8
3rd has s, p & d = 18
4th has s, p, d & f = 32
5. The order of electrons
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d
6. Exceptions – chromium and copper (shift an electron between 4s and 3d
orbitals for stability)
7. Can use shorthand by starting with closest Nobel Gas and building from
there – ex. Strontium [Kr]5s2
8. Count superscripts to determine the element
9. Valence electrons determined by counting electrons in highest energy level
10. Can also show ions – add or subtract appropriate number of electrons
Individual Practice
• Atom Building Game – Lab C-1 “How is
the Periodic Table Organized?”
• Guided Practice from Chemistry book
• Worksheets on Aufbau Principle, Pauli
Exclusion Principle, Hund’s Rule, Orbital
Diagrams, Writing Electron Configurations
Practice Set #1
Practice Set #2
Practice Set #3