Electron Configurations:

Objectives:

1.    Determine the electron configurations of several elements using the principles of orbital energy, orbital capacity, and electron spin.

Key Terms:

electron configuration    orbital diagram

Web Resources:

Notes:

Electron Configurations:

The distribution of electrons in the different electron orbitals is called the electron configuration.  The distribution within the energy levels (n) and suborbitals follows the following principles.

1)    Electrons always fill the available suborbitals based on the suborbital's energy levels (s,p,d,f).
 When electrons fill only the lowest energy orbitals available, the atom is in its ground state. (Atoms are normally found in this state) The location of the electrons can be predicted using the following three rules; A)    Aufbau principle - Electrons are added one at a time to the lowest energy orbitals until all electrons have been accounted for.

(www.iun.edu/.../images/ energy-levels.jpg)

(pirun.ku.ac.th/~b4104056/project/ atom/page/config.gif)

B)    Pauli exclusion principle - Any orbital can hold a maximum of 2 electrons with opposite spins.

(www.chem.ucalgary.ca/courses/ 350/Carey/Ch01/Hund's.gif)

C)    Hund's rule - Electrons occupy equal-energy orbitals so that there are the maximum amount of unpaired electrons. (applies to p, d, & f orbitals)

(www.chem.ucalgary.ca/courses/ 350/Carey/Ch01/Hund's.gif)

All of the p orbitals are filled giving the atom the lowest possible ground state energy.  Additionally, the two p electrons are in paired spins adding repulsion that helps them remain in their ground state.

Electron notation:

The distribution of the electrons can be further defined by listing the electron configuration.  The electron configuration of an atom describes where the electrons are found and what energies they possess.

(www.chem.ufl.edu/~chm2040/Images/ Chapter/Chap_9/c8f7.gif)

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6