The Electron Configuration

• Write the electron configuration for a variety of atoms and ions

• Relate the electron configuration of an element to its valence electron(s) and its position on the periodic table.

Additional KEY TermsShorthand notation

NUCLEUS

1s

2s 2p

3s

3p 3d

4s 4p 4d 4f

Quantum Level

Shapes Total Orbitals

1 s 1s = 1

2 s,p 1s+3p = 4

3 s,p,d 1s+3p+5d = 9

4 s,p,d,f 1s+3p+5d+7f = 16

n n types n2

1. Pauli Exclusion Principle• Electrons are constantly spinning which creates

a magnetic field• Two electrons can occupy the same orbital only

if they have opposite spins

Each orbital (m) of a shape can hold two spinning electrons (s)

n = 1

1s2

n = 22s22p6 n = 33s2 3p6 3d10

OLD way

NEW way

2e- 8e- 18e-

8e-

8e-

2e-

Quantum Level

Shapes Total orbitals e- capacity

1 s 1 = 1 2

2 s,p 1+3 = 4 8

3 s,p,d 1+3+5 = 9 18

4 s,p,d,f 1+3+5+7 = 16 32

n n types n2 2n2

2. Aufbau Principle

Unexcited electrons fill the lowest, most stable, energy orbital available – ground state.

Notice: as you get further from the nucleus the energy

differences are similar enough to mess-up the

“order”

3. Hund ruleElectrons must enter empty orbitals of equal energy first before joining occupied orbitals.

The “get your own room” principle – no one wants a bunkmate

Electron Configuration

Orbital Box Diagrams

1s 2s 2p 3s 3p 3d4s

These are the two ways of representing electron location – we will focus on Electron Configuration

Periodic Table shows orbital filling for the electron configuration of elements.

Draw orbital box and electron config for carbon.

C: 1s2 2s2 2p2

1s 2s 2p

Draw orbital box and electron config for Mg.

Mg: 1s2 2s2 2p6 3s2

1s 2s 2p 3s

First ask yourself “how many total electrons,” then

put them in their correct orbitals

Draw electron config for germanium.

Ge – atomic number 32

Ge: 4s2 3d10 4p2

• Shorthand notation using noble gas “kernels.”

Ge: [Ar] 4s2 3d10 4p2

1s2 2s2 2p6 3s2 3p6

[Ar]

12345

Write the shorthand configurations for Mn and Ag.

Mn: [Ar] 4s2 3d5 Ag: [Kr] 5s2 4d9

Find the last filled Noble Gas to use as the kernel

• Valence configuration includes the electrons in the outer-most or highest quantum level (n).

F = 9 electrons

1s2 2s2 2p5 Valence configuration - 2s2 2p5

Ge = 32 electrons

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2

Valence configuration - 4s2 4p2

It’s not just the last ones, but the total electrons in the outer

quantum level

F-1 = 9 electrons + 1 gained

The ION configuration is 1s2 2s2 2p6

Fe+2 = 26 electrons – 2 lost

The ION configuration is 1s2 2s2 2p6 3s2 3p6 3d6

Valence electrons are removed from the highest quantum level

1s2 2s2 2p5

1s2 2s2 2p6 3s2 3p6 4s2 3d6

Some exceptions to the rule:

• Half-filled and completely filled orbitals have extra stability

• Atoms will “promote” electrons to improve overall stability

Electron Promotion

Look for configurations ending in “p2” ,“p5” OR “d4” ,“d9” - one electron from being half or

complete filled…”

Cr: [Ar] 4s2 3d4 Cu: [Ar] 4s2 3d9

Actual configurations:Cr: [Ar] 4s1 3d5 Cu: [Ar] 4s1 3d10

4s 3d 4s 3d

Electron promotion accounts for multiple ionization states (Fe+2, Fe+3…)

CAN YOU / HAVE YOU?

• Write the electron configuration or orbital box diagrams for a variety of atoms and ions

• Relate the electron configuration of an element to its valence electron(s) and its position on the periodic table.

Additional KEY TermsShorthand notation