1. ELECTRON CONFIGURATION

2. Electron Configuration
Arrangement of electrons in an atom
Ground state electron configuration
Lowest energy arrangement of electrons

3. THREE BASIC RULES

4. AUFBAU PRINCIPLE
The first rule shows the order in which electrons occupy orbitals.
An electron occupies the lowest energy orbital that can receive it
Lowest energy level is the 1s orbital
The 2s orbital is the next highest in energy then the 2p orbitals

5. AUFBAU PRINCIPLE (CONT’D)
Beginning with the third level the energy of the sublevels in different main energy levels begin to overlap
The 4p orbitals will begin to fill after the 3d orbitals are fully occupied

6. PAULI EXCLUSION PRINCIPLE
No two electrons in the same atoms can have the same set of quantum numbers
The two values of the spin quantum numbers allow two electrons of opposite spins to occupy the orbital

7. HUNDI’S RULE
Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron and all electrons in singly occupied orbitals must have the same spin

8. A CLOSER LOOK AT ELECTRONS: WHERE ARE THEY IN THE ATOM?

9. Electrons are located within energy levels, which range from 1 to 7
Electrons are located within energy levels, which range from 1 to 7. The higher the energy the electron is in.....
1. The farther the electron is from the nucleus
2. the more energy the electron has

10. SUBLEVELS
In each energy level, differ from each other by slight differences in energy.
ORBITAL
“Paths” in each sublevel that an electron can travel on

11. Each orbital can hold a maximum of “2” electrons.
In every “s sublevel”, there is 1 orbital, which holds a total of 2 electrons
In every “p sublevel”, there are 3 orbitals, which holds a total of 6 electrons
In every “d sublevel”, there are 5 orbitals, which holds a total of 10 electrons
In every f sublevel, there are 7 orbitals, which hold a total of 14 electrons

12. In what order do orbitals fill up?
Low energy orbitals first, then higher energy orbitals

13. WRITING THE ELECTRON CONFIGURATION FOR AN ATOM

14. The format for the electron configuration is, for example
1 = the energy level
S = the sublevel, or orbital
2 = the number of electrons in that sublevel

15. HOW TO WRITE AN ELECTRON CONFIGURATION

16. Locate the element on the periodic table
Fill the orbitals in the proper order
Check that the total number of electrons you have equals the atomic number for that element.
Examples:
Write the electron configurations for ....

17. Carbon Lithium Sodium Chlorine Potassium Iron 1s2, 2s2, 2p2 1s2, 2s1
1s2, 2s2, 2p6, 3s2, 3p5
Potassium
1s2, 2s2, 2p6, 3s2, 3p6, 4s1
Iron
1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d6

18. Using Shorthand Notation for the Electron Configuration
Put the noble gas that precedes the element in brackets, then continue filling the rest of the orbitals in order as usual.
Examples:
Sodium Potassium
[Ne] 3s1 [Ar] 4s1
Chlorine Iron
[Ne] 3s2, 3p [Ar] 4s2, 3d6

19. The Significance of the Electron Configurations

20. What is the maximum number of valence electrons an atom can have?
Valence Shell
The outermost energy level of an atom
Valence electrons
Electrons in the valence (outer) shell; important because in chemical bonding
What is the maximum number of valence electrons an atom can have? 8
How do each of the noble gases differ from other atoms?
They have a full valence (outer) shell

21. How do noble gases behave?
They are not very reactive (once an atom has a full outer shell, it will not attempt to gain/lose any more electrons)