1. Electron Configurations
Chapter 4 Chm 1.1.3

2. Where are the e- in an atom?
Electron cloud model – probability of finding electrons
Atoms are separated into
Energy Levels (n) (1, 2, 3, 4…etc)
Sublevels (s, p, d and f)
Orbital's (s = 1, p = 3, d= 5, f = 10)

3. Energy Level = n Corresponds to the period (row) the element is in
Ex: H =
period 1 = 1 energy level
C =
period 2 = 2 energy levels
Al =
period 3 = 3 energy levels

4. Sublevel (s, p, d or f) Corresponds to the “block” the element is in S

5. Orbitals An orientation (shape) Each orbital can hold 2 electrons
Each sublevel can have a certain number of sublevels
s = e-
p = 3 (px, py, pz) 6 e-
d = e-
f = e-

6. Principles
Pauli Exclusion Principle – no two electrons can have the same location in the electron
Aufbau Principle – energy levels must be full for e- to go into a higher one
Hunds Rule – electron must fill orbitals one at a time before pairing

7. Electron Configurations
Hydrogen
* period 1 = 1 energy level
* block s = electron is in sublevel s
* orbital = s has 1 orbital
* electron = H has 1
1s ___

8. Helium
* period 1 = 1 energy level
* block s = electrons are in sublevel s
* orbital = s has 1 orbital
* electrons = He has 2
1s ____

9. Lithium
* period 2 – has 2 energy levels (1 and 2)
* block s = highest e- is in s sublevel
* orbital = s has 1 orbital
* electrons = lithium has 3
1s ___ 2s ___

10. Boron
* period 2 = 2 energy levels (1 and 2)
* block p = highest electrons are in sublevel p
* orbital = p has 3 orbitals
* electrons = there are 5
1s ___ 2s ___ 2p ___ ___ ___

11. Fluorine
* period 2 = 2 energy levels (1 and 2)
* block p = highest electrons are in p sublevel
* orbital = p has 3 orbitals
* electrons – F has 9
1s ___ 2s ___ 2p ___ ____ ____

12. Every element’s atoms are just like the one before it just with
Remember …..
Every element’s atoms are just like the one before it just with
1 more electron!

13. Energy Level Sequence Goes in order until you get through 3p
3d is expected next but….
4s has lower energy than 3d (d block is always one less than the period)
e- want to be in LOWEST ENERGY state
Sequence is thrown off after 6s too
4f comes next (f block is always 2 less)

14. Electron Configurations
Orbital notation – orbital's shown, arrows used for electrons
Electron Configuration – only energy level, sublevel and total number of e- are shown
Noble Gas Notation – noble gas symbol in brackets in substituted for lengthy electron configuration