BONDING FORCES AND ENERGIES

As the atoms approach, each exerts forces on the other. These forces are of two types, attractive and repulsive, and the magnitude of each is a function of the separation or interatomic distance. The origin of an attractive force FA depends on the particular type of bonding that exists between the two atoms. Its magnitude varies with the distance, as represented schematically in Figure below:




FIGURE : (a) The dependence of repulsive, attractive, and net forces on interatomic separation fortwo isolated toms. (b) The dependence of repulsive, attractive, and net potential energies on interatomic separation for two isolated atoms.
The net force FN between the two atoms is just the sum of both attractive
and repulsive components; that is,

When FA and FR balance, or become equal, there is no net force; that is,



Sometimes it is more convenient to work with the potential energies between two atoms instead of forces. Mathematically, energy (E) and force (F) are related as:

in which EN, EA , and ER are respectively the net, attractive, and repulsive energies for two isolated and adjacent atoms.
The bonding energy for these two atoms, E0 , corresponds to the energy at this minimum point; it represents the energy that would be required to separate these two atoms to an infinite separation.
Types of Bonding
Primary bonding: e- are transferred or shared Strong (100-1000 KJ/mol or 1-10 eV/atom)
? Ionic Bonding:
A columbic interatomic bond that exists between two adjacent and oppositely charged ions.
Formation of ionic bond:
1. Mutual ionization occurs by electron transfer (remember electronegativity table)
• Ion = charged atom
• Anion = negatively charged atom
• Cation = positively charged atom
2. Ions are attracted by strong columbic interaction
• Oppositely charged atoms attract
Example: NaCl
Na has 11 electrons, 1 more than needed for a full outer shell (Neon)
Cl has 17 electrons, 1 less than needed for a full outer shell (Argon)