Electron Configurations

Bohr Model IssuesWhile the Bohr Model

correctly positions electrons into energy levels, the true locations of electrons aren’t shown.Instead of electrons

following a set circular path around the nucleus, they are randomly found in regions of space we call orbitals.

Quantum Mechanical

ModelThis model uses probability functions to calculate an area of space that takes a specific shape around the nucleus.

The orbital is the region where these electrons are found approximately 90% of the time.

Quantum NumbersPrincipal Quantum

Numbers:Show relative sizes and energy of orbital sublevels

n = 1 (1st level)

n = 2 (2nd level)

n = 3 (3rd level)n = 4 (4th level)

Identifying nWhat is the principal energy level for the outermost electron in the following element?

Identifying nWhat is the principal energy level for the outermost electron in the following element?

Identifying nWhat is the principal energy level for the outermost electron in the following element?

Orbital BasicsDifferent orbitals have different shapes and sizes.

s p d f

Additional shapes are possible for orbitals in the same energy sublevel.

Energy SublevelsThere is a pattern to the

location where the electrons are found on the periodic table.

Orbital SublevelsIn which orbital sublevel

would you find the final electron for the atom below?

A) 4sB) 3sC) 3pD) 2p

Orbital SublevelsIn which orbital sublevel

would you find the final electron for the atom below?

A) 2sB) 3sC) 3pD) 4p

Orbital SublevelsIn which orbital sublevel

would you find the final electron for the atom below?

A) 4dB) 4sC) 3dD) 4p

Orbital SublevelsIn which orbital sublevel

would you find the final electron for the atom below?

A) 5fB) 5dC) 7fD) 7s

Energy Sublevels

The type of orbital being filled determines the number of orbitals available in a sublevel.

s: only 1 orbital per sublevelp: 3 orbitals per subleveld: 5 orbitals per sublevelf: 7 orbitals per sublevel

Once an orbital sublevel is filled, the next electron is placed in the next sublevel up.

Electron Filling Principles1) The Aufbau Principle:

an electron will occupy the lowest energy position possible (Think 2-8-8 Rule)

Electron Filling Principles2) Pauli Exclusion Principle:

A single orbital can hold at most 2 electrons (with opposite spin).

3) Hund’s Rule:An electron will fill an unoccupied orbital in an energy sublevel before sharing an orbital with another electron.

Orbital DiagramsOrbital diagrams use the electron filling principles to show the number of orbitals that are filled, partially filled, or empty.

Arrows represent electrons with up or down spin in an orbital.

Oxygen1s 2s 2p

Orbital Diagram PracticeTrue or False:

the correct orbital diagram for sulfur is shown below

Orbital Diagram PracticeTrue or False:

the correct orbital diagram for vanadium is shown below

Orbital Diagram PracticeTrue or False:

the correct orbital diagram for copper is shown below

An Easier Way…You’ll notice that if you show every electron being filled, larger atoms would take a very long time to write.We have electron

configurations to help simplify that process.

Electron configurations abbreviate an orbital sublevel with the sublevel-type-number notation.

2p4

Electron ConfigurationsFull electron configurations

show all orbital sublevels in the order the electrons are filled up.

Shortened (noble gas) configurations start with the last noble gas electron filled and then the remaining electrons.

1s22s22p63s2

3p3

[Ne]3s23p4

Electron Configuration

PracticeWhich of the following is the correct electron configuration for oxygen?

A) 1s2 2p6

B) 1s2 2s2 2p4

C) 2p4

Electron Configuration

PracticeWhich of the following is the correct electron configuration for potassium?A) 1s2 2s2 2p6 3s1 B) 1s2 2s2 2p6 3s2 3p7

C) 1s2 2s2 2p6 3s2 3p6 4s1

Electron Configuration

PracticeWhich of the following is the correct electron configuration for molybdenum?A) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d4 

B) 1s2 2s2 2p6 3s2 3p6 4s2 4d10 4p6 5s2 5d4

C) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d5  

Short Configuration Practice

Which of the following is the correct short-form electron configuration for silicon?

A) [Ne] 3p2 B) [Ne] 3s2 3p2

C) [Ar] 3s2 3p2

Short Configuration Practice

Which of the following is the correct short-form electron configuration for chromium?

A) [Ar] 4s2 3d4

B) [Kr] 4s2 3d4

C) [Ar] 4s1 3d5

Short Configuration Practice

Which of the following is the correct short-form electron configuration for lead?

A) [Xe]  6s2 4f14 5d10 6p2   

B) [Xe]  6s2 5d10 6p2  

C) [Xe]  6s2 6p2  

Lewis SymbolsLewis symbols show the element symbol surrounded by only electrons that fill the outer s & p orbitals.

Li C Al Cl

Lewis Symbol PracticeDraw the Lewis Symbol for

each of the following atoms:

Ba N

Pb Ag