Electron Configuration Exceptions Examples: Cr, Cu, Ag, and Mo

There are several important exceptions to the general pattern for electron configurations of the elements. In this video we will look four different exceptional configurations: Cr, Mo, Cu, and Ag. Of these, the electron configurations for Chromium (Cr) & Copper (Cu) are the most common exceptions taught in general chemistry.

For these exceptions there are two rules to remember:
• Full-filled d subshells are more stable than partially filled.
• Half-filled d subshells are more stable than less than half filled.


-- Useful Resources --

• Cu Electron Config:    • Electron Configuration for Cu, Cu+, a...  
• Cr Electron Config:    • Electron Configuration for Cr, Cr2+, ...  
• Mo Electron Config:    • How to Write the Electron Configurati...  
• Ag Electron Config:    • How to Write the Electron Configurati...  

• Introduction to Writing Electron Configurations:    • Introduction to Electron Configurations  
• Electron Configurations Chart:    • Using the Electron Configuration Chart  
• Writing Electron Configs Using only the Periodic Table:    • Writing Electron Configurations Using...  
• Order of d and s Orbital Filling: https://eic.rsc.org/Coature/the-troub...

Note that when writing the electron configuration for an atom like Cu, the 3d is usually written before the 4s. Both of the configurations have the correct numbers of electrons in each orbital, it is just a matter of how the electronic configuration notation is written (see below for link to an explanation why).

The configuration notation provides an easy way for scientists to write and communicate how electrons are arranged around the nucleus of an atom. This makes it easier to understand and predict how atoms will interact to form chemical bonds. Knowing the exceptions is also important.