Today we talked about Lewis structures, expanded and incomplete octets, and formal charge.

Athough Lewis structures are great for understanding bond order (length & strength) they do not indicate electron movement or reflect the true 3-D shape of the molecule. Other factors that should be considered are resonance, electron repulsion and electronegativity. After using the basic steps to asseble a Lewis structure, consider the formal charge to determine if you have selected the best structure for the molecule. Expanded octets are allowed only if valence electrons are in n=3 and n=4 because of the 3d and 4p orbitals in n=3, n=4 (2s3s orbitals full) and because n=3,n=4 atoms are bigger than n=2 or n=1 orbitals (due to e/e repulsion).