Quantum Number

• Keep in mind are probabilities of finding electrons in certain places doing certain things(spin).

• n = what energy level (1, 2, 3, 4 . . .)• l = what sub-level (s, p, d, or f)• m = which orbital (s=1; p=3; d=5; f=?)• s = which spin (only two possibilities up or

down)

Pauli Exclusion Principle

• No two electrons ever have the same four quantum numbers in the same atom.

• Just as no two houses have the same address.

How are these organized?

n = 1

n= 2

n = 3

n = 4

Level 1 sublevels

Level 2 sublevels

Level 4 sublevels

Level 3 sublevels

ss

ss

ss

ss

p p

pp

pp

dd

dd ff

Remember: 1s is smaller than 2s, 2s is smaller than 3s, etc.

How about energy?

Which has the most?

How do atoms put their electrons in these sublevels?

• Lowest energy levels are filled first.

• Sublevels are filled “s”, then “p”, then “d”, then “f”.

• Well, sort of...

Orbitals

Pri

ncip

al q

uant

um n

umbe

r 3s 3p 3d

4s 4p 4d 4f

1s

2s 2p

5s 5p 5d 5f

6s 6p 6d 6f

7s 7p 7d 7f

s p d f

1

2

3

4

5

6

7

1s orbital holds two electrons

e-e-

e-e-

Then consider the next orbital: 2s (which also holds only two e-.)

e- e-

e-e-

Then consider the next orbital: 2p there are three of them

(which also hold two e-each)

e- e-

This is one of three.

Electron configuration for … Scandium

• Look up the number of electrons (same as the number of protons).

• Use the diagonal rule.

• Scandium is #21. That means Sc has _____ electrons.

2621

Electron configuration for … Scandium

1262622 3433221 dspspss

21s

Energy level (Principle Quantum #)

# of electrons(add these)

Sublevel

Electron configuration for … Scandium

1262622 3433221 dspspss

Add These

PracticeElectron configurations for:

• Neon

• Aluminum

• Vanadium

12622 33221 pspss1s22s22p6

1s22s22p63s23p1

1s22s22p63s23p64s23d3