Electric Attraction and Repulsion Forces

Procedure Strongly rub a transparency with a piece of paper. Hang both transparency and paper close to each other. Rub two transparencies in a similar fashion on paper bring the transparencies close to each other. 

Observation Initially paper and transparency are strongly attracted, the paper almost sticks to the transparency objects attract if they are oppositely charged. In the second case, both transparencies repel each other similarly charged objects repel each other. 

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Observation Large and small discs attract each other. In the arrangement each large disc is surrounded by four small discs and each small disc surrounded by four large ones (see Fig. 5.19). This structural model can be compared to one layer of the sodium chloride structure. Similarly, salt structures gain stability from the balance of electric attraction and repulsion forces, in relation to the magnets there are magnetic forces. 

The term "affinity" has its roots in very old ideas to the effect that like attracts like and that bodies combine with other bodies because of mutual affection or affinitas. This meaning is employed in Etienne Francois Geoffroy s Table des differents rapports observes entre differentes substances (1718) for replacement reactions.28 However, in the middle of the eighteenth century, Boerhaave spoke of the affinity of a substance for others unlike it, giving the word "affinity" a new meaning. Boerhaave interpreted Geoffroy s table as a representation of Newtonian-type forces of gravitational attraction or electrical attraction and repulsion.29... 

The four forces are gravity, electromagnetism (electrical attraction and repulsion and magnetic forces are explained by the same theory), and the strong and weak nuclear forces. The weak force is... 

If the properties of one ion affect those of the other when they interact, an iterative approach has to be taken until constancy of intermolecular energy is obtained. This is because the dipoles induced in the ions exert counter fields upon the surrounding ions and the resulting change in shape modifies the values obtained for a system conceived as a sum of attractive and repulsive forces of unchanging spherical ions. If such a counter field can be calculated, then equations such as (5.9) can be used without the introduction of a dielectric constant in the Coulomb attractive term. Thus, dielectric constants are empirical devices that make an allowance for counter fields and forces in electrical systems. 

Colloidal particles are subjected to a number of attractive and repulsive forces and the stability of dispersions depends on the interplay of these various forces. The van der Waals attractive forces between particles have their origin in the electron wave fluctuations and are usually effective at close ranges. Electrical double layer interactions stem from the presence of ionized species at the interface and are effective at distances proportional to the double layer thickness for the given... 

Problem Oppositely charged ions are attracted in rock salt crystal (Na+ and Cl-), similarly charged ions repel each other (Na+ and Na+, Cl- and Cl-). The attraction of all ions in salt crystals can be explained by the balance of attraction and repulsion forces. It is difficult to create such a model showing electric forces. It is, however, possible to implement a model for demonstration purposes with a balance of magnetic attraction and repulsion forces which thereby simulates a two-dimensional crystal. 

Van der Waals forces The term van der Waals forces denotes the short-range interactions between closed-shell molecules. Van der Waals forces include attractive forces arising from interactions between the partial electric charges and repulsive forces arising from the Pauli exclusion principle and the exclusion of electrons in overlapping orbitals. A very commonly used potential is the so-called Lennard-Jones (6-12) potential to describe the attractive and repulsive components of van der Waals forces. 

The generation of an aerosol is as varied as the methods for manufacturing macromolecules. All employ some sort of external force to divide the liquid bulk into individual droplets. Some methods employ aerodynamic forces, mechanical vibration, or pressure oscillations, whereas others harness electrical attraction and repulsion. 

Adsorption is based on the energetic properties of solid surfaces. At the solid-fluid interface, attractive and repulsive forces are acting on the molecules of the adsorbate (adsorbed molecules). The most important forces are van der Waals or dispersion forces and electrostatic forces. It will be shown later that the Hamaker constant, the electrical charge, the polarizability of the adsorbent molecules, and the dipole and quadrupole moments as well as the polarizability of the adsorptive molecules are the decisive properties for gas-sohd equilibria. These equilibria describe the relationship between the concentration of the adsorptive in the fluid phase and the loading of the adsorbent Principally speaking, two or more components of a fluid can be adsorbed. 

The intermolecular interactions between species arise from the electronic and quantum nature of atoms. An atom can be viewed as containing a fixed, positively charged nucleus surrounded by a relatively mobile, negatively charged electron cloud. When a molecule is in close enough proximity to another molecule, the electrically charged structure of its atoms can lead to attractive and repulsive forces. The attractive forces include electrostatic forces between point charges or permanent dipoles, induction forces, and dispersion forces. 

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