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