CH301H - Principles of Chemistry I: Honors
Fall 2012, Unique 51390

Lecture Summary, 11 September 2012

Ionic Bonding:  When an atom with low IE and low EA bonds with an atom with high IE and high EA, such as group I or II bonding with group VII, the high EN atom will completely sequester the shared electrons, on the bond will be ionic.  The strength of an ionic bond can be determined by tabulating the energy needed to form each ion and the electrostatic potential energy gained by allowing the ions to interact.  We did this for the reaction

      K + F --> KF

and were able to draw the potential energy curve for the stable KF molecule.  

Covalent Bonding:  Almost all bonds have some covalent character.  The classical model of covalent bonding says that there is a region of space between two interacting nuclei where a shared electron can lower the potential energy of the system, resulting in a stable region of potential energy space.  This is called a "bonding" region.  If the electron is outside that region, it not only does not stabilize the two interacting nuclei, it destabilizes the entire system.  This is called the "antibonding" region.  If an electron is in the bonding region, a stable covalent bond can be formed.  If an electron is in an antibonding region, it will work against formation of a colvalent bond.