Lewis Dot Structures
To understand the why bonding matters and to understand the effect of polarity we need to look beyond individual bonds and think in terms of molecules. Remember that a molecule is two or more atoms bonded together (covalently bonded—compounds that are held together by ionic bonds do NOT have molecules). There are numerous ways to understand the way that atoms join together to form molecules, but in this text we will be focusing on just one of those ways—Lewis Dot Structures.
Before Lewis' time, chemists understood that molecules existed and knew the formulas for many different types of molecules. What Lewis provided was a way to quickly determine the general structure of a molecule, including which atoms were bonded to which and how many electrons were involved in each bond. The system he created can then be used to determine the three-dimensional arrangement of the atoms in the molecule, which allows us to determine the polarity of the entire molecule rather than just of the individual bonds within that molecule.