1. Electron Configuration
Ch. 4 - Electrons in Atoms
Electron Configuration

2. Maximum Number of Electrons In Each Sublevel
Sublevel Number of Orbitals of Electrons s p d f
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 146

3. Electron capacities Electron capacities
Copyright © 2006 Pearson Benjamin Cummings. All rights reserved.

4. Writing Electron Configurations
Way to show the arrangement of electrons in an atom
Parts
1s2
sublevel
# of electrons in that sublevel
Energy level
1s2 2s2 2p4

5. Sublevels 4f 4d 4p 4s n = 4 3d 3p 3s n = 3 Energy 2p 2s n = 2 1s n = 1
1s22s22p63s23p64s23d104p65s24d10…
Electron configuration of an element is the arrangement of its electrons in its atomic orbitals
One can obtain and explain a great deal of the chemistry of the element by knowing its electron configuration 2p 2s
n = 2 1s
n = 1

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

7. Filling Rules for Electron Orbitals
Aufbau Principle: Electrons are added one at a time to the lowest
energy orbitals available until all the electrons of the atom
have been accounted for.
Pauli Exclusion Principle: An orbital can hold a maximum of two electrons.
To occupy the same orbital, two electrons must spin in opposite
directions.
Hund’s Rule: Electrons occupy equal-energy orbitals so that a maximum
number of unpaired electrons results.
*Aufbau is German for “building up”

8. General Rules Aufbau Principle
Electrons fill the lowest energy orbitals first.
“Lazy Tenant Rule”

9. Order in which subshells are filled with electrons2p 3p 4p 5p 6p 3d 4d 5d 6d 4f 5f
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d …

10. Examples
Chlorine
Bromine
Calcium

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

12. Notation
Orbital Diagram 1s 2s 2p O
8e-

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

14. H = 1s1 He = 1s2 Li = 1s2 2s1 Be = 1s2 2s2 C = 1s2 2s2 2p2 S
THIS SLIDE IS ANIMATED
IN FILLING ORDER 2.PPT H
= 1s1 1s He
= 1s2 1s Li
= 1s2 2s1 1s 2s Be
= 1s2 2s2 1s 2s C
= 1s2 2s2 2p2 1s 2s
2px
2py
2pz S
= 1s2 2s2 2p43s23p4 1s 2s
2px
2py
2pz 3s
3px
3py
3pz

15. Fe = 1s1 2s22p63s23p64s23d6 26 Iron has ___ electrons. Arbitrary
2px
2py
2pz 3s
3px
3py
3pz 4s 3d 3d 3d 3d 3d
Arbitrary
Energy Scale 18 32 8 2 1s
2s p
3s p
4s p d
5s p d
6s p d f
NUCLEUS e- e- e- e- e- e- e- e- e- e- e- e- e-
+26 e- e- e- e- e- e- e- e- e- e- e- e- e-

16. Examples
Nitrogen
Aluminum

17. Shorthand Configuration
Element symbol
Electron configuration Ca
[Ar] 4s2 V
[Ar] 4s2 3d3 F
[He] 2s2 2p5 Ag
[Kr] 5s2 4d9 I
[Kr] 5s2 4d10 5p5 Xe
[Kr] 5s2 4d10 5p6 Fe
[He] 2s22p63s23p64s23d6
[Ar] 4s23d6 Sg
[Rn] 7s2 5f14 6d4