Electron Configuration
Electron Configuration
Electron Clouds
Electron cloud
Principal energy levels
Subshells
Orbitals
The electron cloud is made of energy levels
Energy levels are composed of subshells
Subshells have orbitals.
Subshell versus Orbital
Subshell – A set of orbitals with equal energy
Orbital – Area of high probability of the electron being located.
Each orbital can hold 2 electrons
Types of Subshells
Subshell Begins in energy level
Number of equal energy
orbitals
Total number of electrons
possible
s
p
d
f
2
3
4
1
3
5
7
1
6
10
14
2
En
erg
y in
cre
ase
s
What are electron configurations?
They show the grouping and position of electrons in an atom.
Electron configurations use boxes for orbitals and arrows for electrons.
Energy and Subshells
1s
2s
3s
4s
5s
2p
3p
4p
5p
3d
4d
6s
6p5d
4f
Ene
rgy
Subshells are filled from the lowest energy level to increasing energy levels.
Aufbau Principle
Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum
1
The first of 3 rules that govern electron configurations
What does this mean?
Electrons must fill the lowest available subshells and orbitals before moving on to the next higher energy subshell/orbital.
Hund’s Rule
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.
2
How does this work?
If you need to add 3 electrons to a p subshell, add 1 to each before beginning to double up.
Pauli Exclusion Principle
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.
3
“Spin” describes the angular momentum of the electron
“Spin” is designated with an up or down arrow.
How does this work?
If you need to add 4 electrons to a p subshell, you’ll need to double up. When you double up, make them opposite spins.
Determining the Number of Electrons
Charge = # of protons – # of electrons
Atomic number = # of protons
Example:How many electrons does Br-1
have?
-1 = 35 - electrons
Atomic number for Br = 35 = # of protons
Charge = -1
Electrons = 36
Determining the Number of Electrons
Charge = # of protons – # of electrons
Atomic number = # of protons
Example:How many electrons does Br-1
have?
Writing Electron Configurations
Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum1
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.3
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.2
Example:Write the boxes & arrows
configuration for Cl
Writing Electron Configurations
Aufbau Principle: Electrons fill subshells (and orbitals) so that the total energy of atom is the minimum1
0 = 17 - electrons
No charge written Charge is 0
Atomic number for Cl = 17 = # of protons
Electrons = 17
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.3
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.2
1s 2s 2p 3s 3p
4231567910111213141516178
Example:Write the boxes & arrows
configuration for Cl
Sub-Energy Levels
Electron Configuration PT
Arrow-Orbital DiagramsE
ner
gy
1s
2s
2p3p3
s
4s
3d
Electron Configuration Symbols
5f 3
Energy LevelSub-Energy
Level
# of e- in sub-energy
level
K
K: 2s21s2 4s13s22p6 3p6
Bohr Models
vs. e- Configs
Spectroscopic Notation
Spectroscopic Notation
Shorthand way of showing electron configurations
The number of electrons in a subshell are shown as a superscript after the subshell designation
1s 2s 2p 3s 3p
1s2 2s2 2p6 3s2 3p5
Writing Spectroscopic Notation
Determine the number of electrons to place1
Fill in subshells until they reach their max (s = 2, p = 6, d = 10, f = 14).3
Follow Aufbau Principle for filling order2
The total of all the superscripts is equal to the number of electrons.4
0 = 16 - electrons
No charge written Charge is 0
Atomic number for S = 16 = # of protons
Electrons = 161s 2s 2p 3s 3p2 2 6 2 4
2 2 6 2 4+ + + + = 16
Example:Write
spectroscopic notation for
S
Noble Gas Configuration
Noble Gases & Noble Gas Notation
Noble Gas – Group 8 of the Periodic Table. They contain full valence shells.
Noble Gas Notation – Noble gas is used to represent the core (inner) electrons and only the valence shell is shown.
1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 5
4s 2 3d 10 4p 5[Ar]
Br
Spectroscopic
Noble gas
The “[Ar]” represents the core electrons and only the valence electrons are shown
How do you know which noble gas to use to symbolize the core electrons?
Which Noble Gas Do You Choose?
Think: Price is Right.
How do you win on the Price is Right?
By getting as close as possible without going over.
Choose the noble gas that’s closest without going over!
Noble Gas # of electrons
He
Ne
Ar
Kr
Xe
2
10
18
36
54
Noble Gas Notation Example
Determine the number of electrons to place1
Start where the noble gas left off and write spectroscopic notation for the valence electrons3
Determine which noble gas to use2
Example:Write noble gas notation
for As
+
Noble Gas Notation Example
Determine the number of electrons to place1
Start where the noble gas left off and write spectroscopic notation for the valence electrons3
Determine which noble gas to use2
0 = 33 - electrons
No charge written Charge is 0
Atomic number for As = 33 = # of protons
Electrons = 33
[Ar] 4s 3d 4p2 10 3
18 2 10 3+ + = 33Closest noble gas: Ar (18)
Ar is full up through 3p
Example:Write noble gas notation
for As