1. Electron Configurations

2. The Bohr Model Electrons are in fixed orbits.
Orbits are associated with very specific energies, and are called energy levels.

3. The Quantum Mechanical Model
Like Bohr Model, QMM restricts energies of electrons to certain values.
Unlike Bohr Model, QMM does not define an exact path electron takes around the nucleus.
According the QMM, the exact location of an electron cannot be exactly determined at a given time.
Estimates probability of finding an electron in a certain position.
Regions in which electrons are going to be found are called Orbitals

4. Electron Configurations—The Basics
Chemists describe the placement of electrons based on principal energy levels n=1,2,3,4, etc.
Within these energy levels, there are sublevels labeled s, p, d, and f.
Within these sublevels are orbitals
Every orbital can hold 2 electrons.

5. Principal energy levels (shells)
Principal energy levels are assigned values in order of increasing energy
n=1, 2, 3, 4, …
What do the numbers tells us?
Distance from the nucleus increases with increasing n.
Energy increases with an increasing n.

6. Sublevels (subshells)
Within each principal energy level, electrons occupy energy sublevels
Sublevels denoted by the letters s, p, d, f
In terms of energy, s < p < d < f
What do the letters tell us?
Shape of orbitals
s = sphere, p= dumbbell, d = clover leaf

7. Orbitals Each sublevel contains a certain number of orbitals
Orbital = region in which electrons are likely to be found
What else do the letters tell us?
s = 1 orbital
p = 3 orbitals
d = 5 orbitals
f = 7 orbitals

8. Electrons Each orbital can only contain 2 electrons
In order for electrons to occupy the same orbital, they must have opposite spin

9. Orbitals
S sublevel
1 orbital

10. Orbitals
S sublevel
1 orbital
2 e-

11. Orbitals
P sublevel
3 orbitals

12. Orbitals
P sublevel
3 orbitals
6 total e-
2 in each orbital

13. Orbitals
d sublevel
5 orbitals

14. Orbitals
d sublevel
5 orbitals
10 total e-
2 in each orbital

15. Summary Energy Levels Sublevel # of Orbitals # of Electrons 1 1s 2 2s2p 3 6 3s 3p 3d 5 10 4 4s 4p 4d 4f 7 14

16. Summary 8 32 Energy Levels Sublevel # of Orbitals # of Electrons 1 1s2p 3 6 8 3s 3p 3d 5 10 18 4 4s 4p 4d 4f 7 14 32

17. Summary
What is the relationship between energy level and number of sublevels?

18. Summary Energy Level # = # of sublevels
What is the relationship between energy level and number of sublevels?
Energy Level # = # of sublevels

19. Let’s put it together!

20. Let’s put it together!
It was mentioned earlier that increasing n = increasing energy
Not always the case.
Notice 3d is higher energy than 4s.
This is not the only time when that happens!

21. Writing electron configurations in orbital notation
RULES
Aufbau Principle: Electrons fill the lowest possible energy levels first.
Pauli Exclusion Principle: Two electrons in the same orbital have opposite spins.
Hund’s Rule: Electrons fill in separate orbitals of the same subshell (sublevel) with parallel spins before pairing.

22. Writing electron configurations in orbital notation
Examples:
Carbon
Argon:
Vanadium:

23. Writing electron configurations in superscript notation:
See Periodic Table
Use Aufbau Principle: Fill lowest energy levels first

24. Writing electron configurations in superscript notation:
Ex:
Carbon
Argon
Vanadium

25. Writing electron configurations in superscript notation:
Ex:
Carbon: 6e-
1s22s22p2
Argon: 18e-
1s22s22p6 3s23p6
Vanadium: 23e-
1s22s22p6 3s23p64s23d3

26. Kernel configurations:
To shorten, place previous noble gas (8A) in brackets and continue writing configuration.
Ex:
Vanadium: 23 e-
[Ar] 4s23d3
Bromine:
Al:

27. Kernel configurations:
To shorten, place previous noble gas (8A) in brackets and continue writing configuration.
Ex:
Vanadium: 23 e-
[Ar] 4s23d3
Bromine: 35 e-
[Ar] 4s23d104p5
Al: 13 e-
[Ne] 3s23p1

28. Valence shell/valence electrons
The outermost principal energy level of an atom that includes at least one electron is called the valence shell.
The electrons in the valence shell are called valence electrons.
Valence electrons determine properties and reactivity or elements. Very important!

29. Valence shell/valence electrons
How many valence electrons in examples above?
Carbon:
Argon:
Vanadium:

30. Valence shell/valence electrons
How many valence electrons in examples above?
Carbon: 1s22s22p2 = 4 v.e.
Argon: 1s22s22p63s23p6 = 8 v.e.
Vanadium: 1s22s22p63s23p64s23d3 = 2 v.e.

31. Electron Configurations: Special Cases
Writing electron configurations for ions
For cations (+ charge) subtract electrons
For anions (- charge) add electrons
Ex:
Na+ 11 – 1 = 10 e- 1s22s22p6
N = 10 e- 1s22s22p6
*Same as Neon. These are isoelectronic = Same e- configuration*

32. Exceptional configurations:
For d orbitals only
The atom will be at lowest energy (most stable) when the d sublevel is half full or full.
Chromium and Copper Cr, Cu

33. Exceptional configurations:
Chromium and Copper Cr, Cu
Chromium expected configuration:
1s22s22p63s23p64s23d4
Actual Cr Configuration:
1s22s22p63s23p64s13d5 ← HALF FULL
Copper expected configuration:
1s22s22p63s23p64s23d9
Actual Cu Configuration:
1s22s22p63s23p64s13d10 ← FULL