Lewis Structure
A Lewis Structure minimizes the Formal Charge for all atoms
The order of drawing a structure is as follows:
- Know or guess the molecular structure
- Produce a trial structure by drawing bonds by using their common valance requirements (the amount of hydrogens in their hydride)
- Draw bounds for all other atoms (using double bounds if necessary)
- Aim to reach an Octet Configuration for all atoms but recognize that not all atoms will have an octet configuration
Resonance Structures
Structures that is an average of several structures, molecules like ozone
The resonance structure takes the average of the two forms
Breakdown of the Octet Rule
In certain situations the octet rule can be violated
Odd-Electron Molecules
Atoms with odd electrons like nitrogen can not expect to follow the Octet Rule all the time, for example, nitrogen oxide has an odd electron on the nitrogen
Hypovalent Molecules
Molecules like Xeon Difluoride will have more than 8 electrons on the center, this is because the extra electrons are taking space in the hidden d orbitals of the atom
Problems with Lewis Structures
Lewis Structure provide no indication of shape of the molecule
While VSEPR can be used to predict shapes, these predictions are not always accurate, for example Oxygen is predicted as diamagnetic while it is paramagnetic
In addition, many compounds can not be represented by Lewis Structures without the use of Resonance Structures
Diamagnetic: Contains no unpaired electrons
Paramagnetic: Contains unpaired electrons and is attracted to magnets