1. E LECTRON C ONFIGURATIONS 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

2. E LECTRON C ONFIGURATIONS The distribution of electrons in the different electron orbitals is called the electron configuration. Energy level is listed 1 st Orbital shape is listed 2 nd The number or electrons in the orbital subsystem is listed 3 rd The orbital diagram lists each electron and its spin based on three rules by Aufbau, Pauli, and Hund.

3. A UFBAU PRINCIPLE Electrons are added one at a time to the lowest energy orbitals until all electrons have been accounted for.

4. P AULI EXCLUSION PRINCIPLE Any orbital can hold a maximum of 2 electrons with opposite spins.

5. H UND ' S RULE Electrons fill equal-energy orbitals so that there are the maximum amount of unpaired electrons. (applies to p, d, & f orbitals) Otherwise stated, electrons are unpaired before they are paired All of the p orbitals are filled giving the atom the lowest possible ground state energy. Note that the 3 p electrons are in paired spins adding repulsion that helps them remain in their ground state.

6. E LECTRON 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. The abbreviated electron configuration takes advantage of the noble gas core. The noble gas core lists the noble lists the noble gas of the previous energy level and ALL electrons in orbitals that follow. Xe = 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 4 s 2 3 d 10 4 p 6 5 s 2 4 d 10 5 p 6 or [Kr]5 s 2 4 d 10 5 p 6