1. Electron Configuration
Electrons in Atoms
Electron Configuration

2. General Rules Pauli Exclusion Principle
Each orbital can hold TWO electrons with opposite spins.

3. General Rules Aufbau Principle
Electrons fill the lowest energy orbitals first.
“Lazy Tenant Rule”
Energy levels overlap
Expected order:
1s 2s 2p 3s 3p 3d 4s 4p 4d 4f...
Actual order:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f...

4. General Rules WRONG RIGHT Hund’s Rule
Within a sublevel, place one e- per orbital before pairing them.
“Empty Bus Seat Rule”
WRONG
RIGHT

5. S 16e- 1s2 2s2 2p6 3s2 3p4 S 16e- [Ne] 3s2 3p4 Orbital Notation
Longhand Configuration
S 16e-
1s2
2s2
2p6
3s2
3p4
Core Electrons
Valence Electrons
Shorthand Configuration
S 16e- [Ne] 3s2 3p4

6. Orbital Notation
Shows the arrangement of electrons in orbitals within a sublevel.
Use squares to represent orbitals.
Arrow up represents 1 electron.
Arrow up and arrow down represents 2 electrons.

7. 1s2 2s2 2p4 O Orbital Notation 1s 2s 2p 8e- Orbital Diagram
Electron Configuration
1s2 2s2 2p4

8. Orbital Diagrams for Nickel 28 1s 2s 2p 3s 3p 4s 3d 2s 2p 3s 3p 4s 3d 1s
Excited State 2s 2p 3s 3p 4s 3d 1s
Pauli Exclusion 2s 2p 3s 3p 4s 3d 1s
Hund’s Rule

9. Periodic Patterns s p d (n-1) f (n-2) 1 2 3 4 5 6 7 6 7
© 1998 by Harcourt Brace & Company

10. Electron Filling in Periodic Tables s s s H
1s1 He
1s2 H
1s1 p p 1 1 Li
2s1 Be
2s2 B
2p1 C
2p2 N
2p3 O
2p4 F
2p5 Ne
2p6 2 2 Na
3s1 Mg
3s2 d d Al
3p1 Si
3p2 P
3p3 S
3p4 Cl
3p5 Ar
3p6 3 3 K
4s1 Ca
4s2 Sc
3d1 Ti
3d2 V
3d3 Cr
3d5 Mn
3d5 Fe
3d6 Co
3d7 Ni
3d8 Cu
3d10 Zn
3d10 Ga
4p1 Ge
4p2 As
4p3 Se
4p4 Br
4p5 Kr
4p6 4 4 Rb
5s1 Sr
5s2 Y
4d1 Zr
4d2 Nb
4d4 Mo
4d5 Tc
4d6 Ru
4d7 Rh
4d8 Pd
4d10 Ag
4d10 Cd
4p1 In
5p1 Sn
5p2 Sb
5p3 Te
5p4 I
5p5 Xe
5p6 5 5 Cs
6s1 Ba
6s2 Hf
5d2 Ta
5d3 W
5d4 Re
5d5 Os
5d6 Ir
5d7 Pt
5d9 Au
5d10 Hg
5d10 Tl
6p1 Pb
6p2 Bi
6p3 Po
6p4 At
6p5 Rn
6p6 6 6 * * Fr
7s1 Ra
7s2 Rf
6d2 Db
6d3 Sg
6d4 Bh
6d5 Hs
6d6 Mt
6d7 7 7 W W f f La
5d1 Ce
4f2 Pr
4f3 Nd
4f4 Pm
4f5 Sm
4f6 Eu
4f7 Gd
4f7 Tb
4f9 Dy
4f10 Ho
4f11 Er
4f12 Tm
4f13 Yb
4f14 Lu
4f114 * * Ac
6d1 Th
6d2 Pa
5f2 U
5f3 Np
5f4 Pu
5f6 Am
5f7 Cm
5f7 Bk
5f8 Cf
5f10 Es
5f11 Fm
5f14 Md
5f13 No
5f14 Lr
5f14 W W

11. Periodic Patterns Period # energy level (subtract for d & f)
A/B Group #
total # of valence e-
Column within sublevel block
# of e- in sublevel

12. 1s1 Periodic Patterns 1st column of s-block 1st Period s-block
Example - Hydrogen
1s1
1st column of s-block
1st Period
s-block

13. Periodic Patterns p s d (n-1) f (n-2) Shorthand Configuration
Core e-: Go up one row and over to the Noble Gas.
Valence e-: On the next row, fill in the # of e- in each sublevel. s
d (n-1)
f (n-2) p

14. Periodic Patterns
Example - Germanium
[Ar]
4s2
3d10
4p2

15. Stability Full energy level Full sublevel (s, p, d, f)
Half-full sublevel

16. Stability (Honors Only)
Electron Configuration Exceptions
Copper
EXPECT: [Ar] 4s2 3d9
ACTUALLY: [Ar] 4s1 3d10
Copper gains stability with a full d-sublevel.

17. Stability (Honors Only)
Electron Configuration Exceptions
Chromium
EXPECT: [Ar] 4s2 3d4
ACTUALLY: [Ar] 4s1 3d5
Chromium gains stability with a half-full d-sublevel.

18. Stability 1+ 3+ NA 3- 2- 1- 2+ Ion Formation
Atoms gain or lose electrons to become more stable.
Isoelectronic with the Noble Gases. (No charge) 1+ 3+ NA 3- 2- 1- 2+

19. O2- 10e- [He] 2s2 2p6 Stability Ion Electron Configuration
Write the e- config for the closest Noble Gas
EX: Oxygen ion  O2-  Ne
O e [He] 2s2 2p6