Knowing that atoms strive to achieve a full valence shell (generally known as the Octet Rule) we may use the Periodic Table to predict how this will occur within the basic patterns of ionic (electrons transferred), covalent (electrons shared), and polar covalent (electrons shared but unequally). The first two are covered extensively in General Chemistry with the latter becoming more important in Organic. For the most part, the nature of bonding between atoms is predictable from electronegativity (E.N.) values, the trends of which come from the Periodic Table, but knowledge of which can be very useful. Elements on the left (low E.N.) give electrons away to elements on the right (higher E.N.), while elements that are closer together (similar E.N.) tend to form covalent bonds. What can be confusing is when molecules contain both types of bonding, however those patterns are also predictable from electronegativity values. Let’s first consider the four examples shown below. How do we expect each of the atoms to communicate within the molecules?