Electron Configurations of Atoms

Ground State and Valence Shell Electron Configuration.

In general chemistry, you learned to write the ground state and valence shell electron configurations.  Here is the procedure you used.  In this example, we will determine the ground-state electron configuration for a Carbon atom.

1. Find the atomic or proton number from the periodic table (carbon = 6).
2. Using Aufbau's principle you begin filling the orbitals from the bottom up (i.e. lowest energy first).  In the diagram below you start at the top with the 1s orbital and then 2s and then 2p then 3s etc. 

   

3. Recall that there are 3 degenerate p orbitals and 5 d orbitals.  Remember only two electrons per orbital maximum is allowed and their spins must be opposite (Pauli Exclusion Principle).  Degenerate orbitals are filled halfway until all are half-filled (Hund's rule of maximum multiplicity).
   So for a carbon atom, we have 1s²2s²2p_x¹2p_y¹ as the ground state configuration.  You should be able to answer basic questions related to this.

You can simply write this as 1s²2s²2p².  The valence shell configuration is 2s²2p^2, which is the electrons in the outer shell.

Practice Time