Chemical bonds Attractive forces that energy

The adsorption action of activated carbon may be explained in terms of the surface tension (or energy per unit surface area) exhibited by the activated particles whose specific surface area is very large. The molecules on the surface of the particles are subjected to unbalanced forces due to unsatisfied bonds and this is responsible for the attachment of other molecules to the surface. The attractive forces are, however, relatively weak and short range, and are called Van der Waals forces, and the adsorption process under these conditions is termed as a physical adsorption (physisorption) process. In this case, the adsorbed molecules are readily desorbed from the surface. Adsorption resulting from chemical interaction with surface molecules is termed as chemisorption. In contrast to the physical process described for the adsorption on carbon, the chemisorption process is characterized by stronger forces and irreversibility. It may, however, be mentioned that many adsorption phenomena involve both physical and chemical processes. They are, therefore, not easily classified, and the general term, sorption, is used to designate the mechanism of the process. 

We are all familiar with forces between bodies on a macroscopic scale. If one sits at their desk on earth pondering the view and inadvertently lets go of their lunch sandwich it falls until it lands on your manuscript, your lap or the floor—right Better yet, a cannonball and a softball fall at the same rate. It is the definition of gravity . Long after the Tower of Pisa experiments, we discovered why the moon is in seemingly stable orbit around the earth and the earth around the sun is related to forces between bodies. We are also familiar with electrostatic forces and their effects. Dust from the air in the room is attracted to the screen of everyone s TV because of the electrostatic charge it develops. It would seem reasonable that attraction occurs on a smaller scale and even on a molecular scale that does not involve energies on the order of true chemical bonds. 

The problem of recovery leads to the question of hardness. Hard substances have a high number of strongly directed, covalent chemical bonds per unit volume. Soft substances generally have fewer bonds per unit volume or bonds that are weak or weakly directed, such as ionic or dipole attractive forces. Bond energy per unit volume has the same dimensions as pressure (force per unit area), and a plot of hardness measured by the Knoop indenter versus the bond energy per molar volume for various substances is essentially linear, provided that one chooses substances for which the bonding is predominantly of one type (i.e., not mixed, as in graphite or talc). 

This famous, but underutilized, theorem provides an unerring guide to the examination of chemical interactions in Born-Oppenheimer molecules where concepts such as the chemical bond, bond energy and chemical structure retain their classical meaning. Given that kinetic energy of the electrons does not depend on the fixed nuclear coordinates it is readily demonstrated [59] that the force of attraction between the nuclei and the electronic charge... 

Attractive forces operate between all atoms, but unless the potential energy minimum is at least of the order of RT, the two atoms will not be able to withstand the disruptive influence of thermal energy long enough to result in an identifiable molecule. Thus we can say that a chemical bond exists between the two atoms in H2. The weak attraction between argon atoms does not allow Ar2 to exist as a molecule, but it does correspond to the van Der Waals force that holds argon atoms together in the liquid and solid. 

---