1. Electron Configuration
Chemistry 11
Ms. McGrath

2. The Uncertainty Principle
It is inherently impossible for us to know simultaneously both the exact momentum of electrons and their exact location in space
ie. we anticipate that it is not possible to determine exactly where an electron is located at a specific time

3. Electron Configuration
Recall
The Bohr model assumes the electrons are in a circular orbit of some particular radius around the nucleus
In the quantum-mechanical model (what we are looking at today), the electrons’ location cannot be described so simply
In the quantum-mechanical model, we speak of the probability that the electron will be in a certain region of space at a given instant

4. Electron Configuration
Recall that at this point, our construction of the atom is the following:
comprised of electrons, neutrons, and protons
neutrons and protons are found in the nucleus
electrons are present in orbits (energy levels or shells)
each orbit contains orbitals (spaces where electrons are likely to be found)

5. Electron Configuration Orbitals (s, p, d, f)
s Orbital
The first orbit (or shell) only has an “s” orbital
This orbital is spherical and can hold 2 electrons
This orbital is in every energy level

6. Electron Configuration Orbitals (s, p, d, f)
p Orbital
This orbital is said to be dumbbell shaped
It has 3 sub orbitals, each of these sub orbitals can hold 2 electrons (so the p orbital can hold a total of 6 electrons)
The p orbital occurs in energy levels 2 and above

7. Electron Configuration Orbitals (s, p, d, f)
d Orbital
The d orbital is composed of 5 sub orbitals, each of these sub orbitals can hold 2 electrons (so the d orbital can hold a total of 10 electrons)
The d orbital occurs in energy levels 3 and above

8. Electron Configuration Orbitals (s, p, d, f)
f Orbital
The f orbital is composed of 7 sub orbitals, each of these sub orbitals can hold 2 electrons (so the f orbital can hold a total of 14 electrons)
The f orbital occurs in energy levels 4 and above

9. Electron Configuration
It is important to know the order in which the electrons are placed:

10. Electron Configuration

11. Electron Configuration

12. Electron Configuration
Notice when we get to period 4 (the 4th row) we fill the 4s orbital then the 3rd orbital
The f orbitals (in the Lanthanides and Actinides) can be inserted after the 6th and 7th s orbitals.

13. Electron Configuration
There is one more principle we must understand before communicating electron configuration - Aufbau Principle - this principle can be summarized in the following statements and is true for nearly all atoms.
Electrons will occupy the lower energy level orbital first
Electrons will fill each sub orbital with one electron before filling any suborbital with two electrons (Hund’s Rule)

14. Electron Configuration
There are three methods to express electron arrangement:
Energy Level Diagrams (Aufbua diagram)
Electron Configuration
Noble Gas Notation

15. Energy Level Diagrams (Aufbau diagram)

16. Energy Level Diagrams Class Activity
draw out the energy level diagrams for the following elements:
Hydrogen Barium
Helium Lanthanum
Carbon Lutetium
Oxygen Hafnium
Xenon
Cesium

17. spdf Notation
Physicists and chemists use a standard notation to indicate the electron configurations of atoms.
The notation consists of a sequence of atomic orbital labels specifying the orbit, the type of orbital within that orbit, then an superscript indicating the number of electrons present in that orbital.

18. spdf Notation Examples
hydrogen has one electron which is in the s orbital of the first shell, so its configuration is written 1s1
lithium has three electrons in total its configuration is written 1s2 2s1
phosphorus has fifteen electrons in total, its configuration is written 1s2 2s2 2p6 3s2 3p3

19. spdf Notation Class Activity
write out the spdf notation for the following elements:
Hydrogen Barium
Helium Lanthanum
Carbon Lutetium
Oxygen Hafnium
Xenon
Cesium

20. Noble Gas Notation This is an abbreviated notation
All but the last few subshells are identical to those of one the noble gases so we can make use of this
Note: A noble gas cannot have its own notation,

21. Noble Gas Notation Example
Phosphorus (which has fifteen electrons) differs from neon (1s2 2s2 2p6) only by the presence of a third shell. The electron configuration of neon is pulled out, and phosphorus is written as follows:
Phosphorus: [Ne] 3s2 3p3

22. Noble Gas Notation Class Activity
write out the Noble Gas Notation for the following elements:
Hydrogen
Helium
Carbon
Oxygen
Xenon
Cesium