1. Chapter 5: Electrons in Atoms
Sec. 2: Electron Arrangements in Atoms

2. Electron Configurations
The way that …
Three rules govern how electrons are arranged: 1. 2. 3.

3. Aufbau Principle Electrons fill…
An orbital may not have any electrons until…
_______ of each energy level are always filled first
NOTE: The orbitals of one energy level can ….

4. Pauli Exclusion Principle
An electron orbital can hold up to ___ electrons.
The 2 electrons in an orbital must have __________ _______.
An orbital and its electrons can be represented by ______________________.

5. Hund’s Rule
Electrons occupy orbitals of the same _______ _______ with electrons of the same ______ first.
Therefore, within an orbital electrons are first ________, and once all orbitals are filled with one electron, electrons become _______.

6. Practice Look at your handout “Electron Configurations & Periodicity.
Using arrows, fill in the orbital diagram for the elements argon, magnesium and nitrogen.

7. Hund’s Rule Electron Configurations Convenient way to…. Write1. 2. 3.
For example
Fluorine

8. Practice Look at your handout “Electron Configurations & Periodicity.
Write electron configurations for the elements argon, magnesium, and nitrogen.

9. Order in which electrons fill orbitals

10. Exceptions to Electron Configurations
Full sublevels are ...
Half filled sublevels are…
Electron configurations of atoms will change to become..
These are slight exceptions to the_________.

11. Exceptions to Electron Configurations
Consider the electron configuration of Chromium (Cr)
-You would expect the configuration to be
_______________________, but this is an unstable configuration.
-Instead the configuration is _______________________, so that the d sublevel is half filled.

12. Practice
The expected configuration of Copper (Cu) is 1s22s22p63s23p64s23d9.
Change the configuration for copper to make it a more stable atom.