1. Electron configuration REVIEW
AP CHEMISTRY
ALLEN
UNIT 1 – THE ATOM

2. Electron Energy Level Notes
Please read through powerpoint and complete examples on last slide.
BACKGROUND:
Electrons do not travel around the nucleus of an atom in orbits
They are found in energy levels at different distances away from the nucleus. (kind of like shells or layers).

3. The Quantum Mechanical Model of the Atom (cont.)
The wave function predicts a three-dimensional region around the nucleus called the atomic orbital.

4. Hydrogen Atomic Orbitals
Electrons cannot exist between energy levels (just like the rungs of a ladder).
Principal quantum number (n) indicates the relative size and energy of atomic orbitals.
n specifies the atom’s major energy levels, called the principal energy levels.

5. Electron Energy Level Notes
Energy levels are broken up into sublevels:
There are at least 4 possible types of sublevels—given labels: s, p, d, or f

6. Hydrogen Atomic Orbitals (cont.)
Energy sublevels are contained within the principal energy levels.

7. Electron Energy Level Notes
Only a certain number of electrons may exist in an energy level, but the number varies. It can be determined by:
# of electrons in level = 2 x (# of energy level)2
Therefore:
energy level 1 = 2 (1)2 = 2
energy level 2 = 2 (2)2 = 8
energy level 3 = 18
energy level 4 = 32
etc...

8. Electron Energy Level Notes
In each energy level, electrons fill sublevels in a certain order
Level 1:
only has one s sublevel (a spherical shape)
2 electrons may fit in this sublevel--each one has an opposite “spin”, allowing them to take up the same space
Pauli exclusion principle—no more than 2 electrons may be found in the same orbital (“orbital” means a particular location)

9. s-Orbital Image

10. Electron Energy Level Notes
has two sublevels: s and p
2 electrons in s
there are 3 different p orbitals, and may hold 2 electrons each—6 total. (look at shape on p imagine how they can fit together)
total of 8 overall in Level 2

11. p-Orbital Image

12. Electron Energy Level Notes
has 3 sublevels: s, p, and d
2 electrons in s
6 electrons in p
there are 5 different d orbitals, and 2 electrons can fit in each—total of (look at picture of d orbitals, imagine how they can fit together)
total of 18

13. d-orbital notes

14. Hydrogen Atomic Orbitals (cont.)
Each energy sublevel relates to orbitals of different shape.

15. Image of orbitals

16. Electron Energy Level Notes
has 4 sublevels: s, p, d , and f
2 electrons in s
6 electrons in p
10 electrons in d
14 electrons in f (7 different orbitals for f)
total of 32

17. Hydrogen Atomic Orbitals (cont.)

18. Electron Energy Level Notes
The order that electrons fill up orbitals does not follow the logical order of all 1’s, then all 2’s, then all 3’s, etc.
Why? Overlapping of orbitals changes the energy level associated with them

19. Electron Energy Level Notes
There is no need to memorize this order, an easier way is to use the periodic table--it is arranged to show how these orbitals are filled.

20. Ground-State Electron Configuration
The arrangement of electrons in the atom is called the electron configuration.
The aufbau principle states that each electron occupies the lowest energy orbital available.

21. Ground-State Electron Configuration (cont.)
The Pauli exclusion principle states that a maximum of two electrons can occupy a single orbital, but only if the electrons have opposite spins.
Hund’s rule states that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same energy level orbitals.

22. Electron Energy Level Notes
Hund’s rule is used for filling orbitals with electrons. It states that only one electron will be put in each orbital of a sublevel until all of them are filled, and after that, they may be paired up until the sublevel is full.

23. Look at the last column for electron configurations of first 10 elements

24. Noble Gas Configurations
Noble gas notation uses noble gas symbols in brackets to shorten inner electron configurations of other elements.

25. Valence Electrons
Valence electrons are defined as electrons in the atom’s outermost orbitals—those associated with the atom’s highest principal energy level.
Electron-dot structure consists of the element’s symbol representing the nucleus, surrounded by dots representing the element’s valence electrons.

26. Valence Electrons

27. Practice Problems: