Quantum Mechanical Model:Quantum Mechanical Model:Electron ConfigurationsElectron Configurations

Chemistry 11Chemistry 11

Electron ConfigurationsElectron Configurations It is the nature of things to seek the lowest It is the nature of things to seek the lowest

possible energy.possible energy. High energy systems are unstable and tend to High energy systems are unstable and tend to

lose energy in order to become more stable.lose energy in order to become more stable. In terms of the atom, electrons and the nucleus In terms of the atom, electrons and the nucleus

interact to form the most stable arrangement interact to form the most stable arrangement possible.possible.

Electron Configuration:Electron Configuration:

The ways in which electrons are arranged The ways in which electrons are arranged around the nuclei of atoms.around the nuclei of atoms.

Rules to RememberRules to Remember

ThreeThree rules govern the filling of atomic orbitals by rules govern the filling of atomic orbitals by electrons within the principle energy levels.electrons within the principle energy levels. AufbauAufbau Principle Principle Pauli ExclusionPauli Exclusion Principle Principle Hund’sHund’s Rule Rule

Aufbau PrincipleAufbau Principle Electrons enter orbitals of Electrons enter orbitals of lowestlowest energy first energy first The various orbitals within a sublevel of principle The various orbitals within a sublevel of principle

energy level are always equal.energy level are always equal. Within a principle energy level, the Within a principle energy level, the “s”“s” orbital is orbital is

always the lowest energy level.always the lowest energy level. The range of energy levels within a principle energy The range of energy levels within a principle energy

level can level can overlapoverlap the energy levels of an adjacent the energy levels of an adjacent principle energy level.principle energy level.

Using the Aufbau PrincipleUsing the Aufbau Principle

Note:4s orbital is lower in energy than 3d.4f orbital is lower in energy than 5d.As you can see from the diagramthe filling order is as follows:1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s

Energy Level Energy Level TemplateTemplate

Pauli Exclusion PrinciplePauli Exclusion Principle An atomic orbital contains a maximum of 2 electronsAn atomic orbital contains a maximum of 2 electrons In order to occupy the same orbital, these electrons In order to occupy the same orbital, these electrons

must have opposite spins (clockwise and counter must have opposite spins (clockwise and counter clockwise)clockwise)

Vertical arrows are used to show directions of spinsVertical arrows are used to show directions of spins Paired electronsPaired electrons

An Easy Way to RememberAn Easy Way to Remember

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

1s2 holds 2 electrons

Fill the Orbitals From the Bottom-upFill the Orbitals From the Bottom-up

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

1s2 2s2 holds 4 electrons

Fill the Orbitals From the Bottom-upFill the Orbitals From the Bottom-up

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

1s2 2s2 2p6 3s2 holds 12 electrons

Fill the Orbitals From the Bottom-upFill the Orbitals From the Bottom-up

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

1s2 2s2 2p6 3s2 3p6 4s2 holds 20 electrons

Fill the Orbitals From the Bottom-upFill the Orbitals From the Bottom-up

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2

holds 38 electrons

Fill the Orbitals From the Bottom-upFill the Orbitals From the Bottom-up

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2

holds 56 electrons…and so on!

Hund’s RuleHund’s Rule

When electrons occupy orbitals of equal When electrons occupy orbitals of equal energy, one electron enters each orbital until energy, one electron enters each orbital until all orbitals contain all orbitals contain oneone electron with electron with parallelparallel spins.spins.

Second electrons then add themselves to the Second electrons then add themselves to the orbital to “orbital to “pairpair” their spins” their spins

Px Py Pz

Using Hund’s RuleUsing Hund’s Rule

When electrons occupy orbitals of equal When electrons occupy orbitals of equal energy they don’t pair up until they have to.energy they don’t pair up until they have to.

Let’s determine the electron configuration for Let’s determine the electron configuration for Phosphorus…Phosphorus…energyenergy level diagramslevel diagrams

Need to account for 15 electronsNeed to account for 15 electrons

The first to electrons go into the 1s The first to electrons go into the 1s orbitalorbital

Notice the opposite spinsNotice the opposite spins Only 13 moreOnly 13 moreIn

crea

sing

ene

rgy

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

The next electrons go into the 2s The next electrons go into the 2s orbitalorbital

only 11 moreonly 11 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

The next electrons go into the 2p orbital

Only 5 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

The next electrons go into the 3s orbital

Only 3 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

The last three electrons go into the 3p orbitals.

They each go into separate shapes 3 unpaired electrons 1s22s22p63s23p3 In

crea

sing

ene

rgy

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

Remember the following:Remember the following: Lowest energy to higher energy.Lowest energy to higher energy. Adding electrons can change the energy of the Adding electrons can change the energy of the

orbital.orbital. Half filledHalf filled orbitals have a orbitals have a lowerlower energy. energy. Makes them more stable.Makes them more stable. Changes the filling orderChanges the filling order