A Lewis Structure is a visual representation of the bonding and electron distribution in a molecule. It uses symbols to show the number of valence electrons and the connectivity of atoms in a molecule.
To draw a Lewis Structure, first determine the total number of valence electrons in the molecule. Then, determine the central atom and its surrounding atoms. Place the valence electrons around the atoms in pairs, making sure to follow the octet rule. If there are any remaining electrons, place them on the central atom.
The octet rule states that atoms tend to lose, gain, or share electrons in order to achieve a stable configuration with 8 valence electrons, similar to the noble gases. This rule applies to most elements, except for hydrogen, which only needs 2 valence electrons.
Resonance refers to the phenomenon where a molecule can have multiple Lewis Structures that are equally valid. This is due to the delocalization of electrons within the molecule, resulting in the same overall charge and bond lengths. Resonance structures are represented with double-headed arrows between them.
The most stable resonance structure is determined by following the rules of formal charge. The most stable structure is the one with the lowest overall formal charge, with negative charges on the more electronegative atoms and positive charges on the less electronegative atoms.