1. Electron Configuration
Mapping the electrons

2. Electron Configuration
The way electrons are arranged around the nucleus.

3. Quantum Mechanical Model
1920’s-1930’s
Werner Heisenberg (Uncertainty Principle)
Louis de Broglie (electron has wave properties)
Erwin Schrodinger (mathematical equations using probability, quantum numbers)

4. Heisenberg uncertainty principle
it is impossible to determine simultaneously both the position and velocity of an electron or any other particle with any great degree of accuracy or certainty.

5. Erwin Schroedinger
Formulated equation that describes behavior and energies of subatomic particles.
Incorporates both particle and wave behavior in terms of wave function:
is proportional to the probability of finding an electron.

6. Erwin Schroedinger (cont’d)
Leads to Quantum Mechanics: we cannot pinpoint an electron in an atom but we can define the region where electrons can be in a particular time……. called a “probability map”….a 3-dimensional area in space called an ORBITAL

7. Principal Quantum Number, n
Indicates main energy levels
n = 1, 2, 3, 4…
Each main energy level has sub-levels
s p d f

8. Orbital Quantum Number, ℓ (Angular Momentum Quantum Number)
Indicates shape of orbital sublevels
ℓ = n-1
ℓ sublevel
0 s
1 p
2 d
3 f
4 g

9. electron’s energy depends principally on this
Quantum numbers and orbital energies Each electron in an atom has a unique set of quantum numbers to define it { n, l, ml, ms }
n = principal quantum number
electron’s energy depends principally on this
l = azimuthal quantum number
for orbitals of same n, l distinguishes different shapes (angular momentum)
ml = magnetic quantum number
for orbitals of same n & l, ml distinguishes different orientations in space
ms = spin quantum number
for orbitals of same n, l & ml, ms identifies the two possible spin orientations
Unit 6- Atomic Electon Configurations and Periodicity 9

10. Energy level Sublevel # of orbitals/sublevel
n = 1 1s (l = 0) 1 (ml has one value)
n = 2 2s (l = 0) 1 (ml has one value)
2p (l = 1) 3 (ml has three values)
n = 3 3s (l = 0) 1 (ml has one value) 3p (l = 1) 3 (ml has three values) 3d (l = 2) 5 (ml has five values)
n = principal
quantum
number
(energy)
ml = magnetic
quantum
number
(orientation)
l = azimuthal
quantum
number
(shape)
Unit 6- Atomic Electon Configurations and Periodicity 10

11. Concept: Each electron in an atom has a unique set of quantum numbers to define it { n, l, ml, ms }11

12. The principle quantum number, n, determines the number of sublevels within the principle energy level.

13. Orbital
The space where there is a high probability that it is occupied by a pair of electrons.
Orbitals are solutions of Schrodinger’s equations.

14. Orbitals

15. Visualizing the orbitals
s orbitals are spherical
p orbitals are “dumbell” shaped
d and f are harder to visualize

16. Orbitals in Sublevels Sublevel # Orbitals # electrons s 1 2 p 3 6d f

17. Three rules are used to build the electron configuration:
Aufbau principle
Pauli Exclusion Principle
Hund’s Rule

18. Aufbau Principle
Electrons occupy orbitals of lower energy first.

19. Orbital Diagram

20. Filling Order diagram

21. -Pauli Exclusion Principle (Wolfgang Pauli, Austria, 1900-1958) -Electron Spin Quantum Number
An orbital can hold only two electrons and they must have opposite spin.
Electron Spin Quantum Number (ms):
+1/2, -1/2

22. Hund’s Rule
In a set of orbitals, the electrons will fill the orbitals in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons).
Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

23. Orbital Diagram for Hydrogen

24. Orbital Diagram for Helium

25. Orbital Diagram for Lithium

26. Orbital Diagram for Beryllium

27. Orbital Diagram for Boron

28. Orbital Diagram for Carbon

29. Orbital Diagram for Nitrogen

30. Orbital Diagram

31. Notations of Electron Configurations
Standard
Shorthand

32. Orbital Diagram for Fluorine

33. Standard Notation of Fluorine
Number of electrons
in the sub level 2,2,5
1s2 2s2 2p5
Main Energy Level Numbers 1, 2, 2
Sublevels

34. Noble Gas Notation
Use the last noble gas that is located in the periodic table right before the element.
Write the symbol of the noble gas in brackets.
Write the remaining configuration after the brackets.
Ex: Fluorine: [He] 2s2 2p5

35. Blocks in the Periodic Table