Electrical repulsion

Although it is hard to draw a sharp distinction, emulsions and foams are somewhat different from systems normally referred to as colloidal. Thus, whereas ordinary cream is an oil-in-water emulsion, the very fine aqueous suspension of oil droplets that results from the condensation of oily steam is essentially colloidal and is called an oil hydrosol. In this case the oil occupies only a small fraction of the volume of the system, and the particles of oil are small enough that their natural sedimentation rate is so slow that even small thermal convection currents suffice to keep them suspended for a cream, on the other hand, as also is the case for foams, the inner phase constitutes a sizable fraction of the total volume, and the system consists of a network of interfaces that are prevented from collapsing or coalescing by virtue of adsorbed films or electrical repulsions. 

Now our nuclear model suffices. We can build up the atoms for all elements. Each atom has a nucleus consisting of protons and neutrons. The protons are responsible for all of the nuclear charge and part of the mass. The neutrons are responsible for the rest of the mass of the nucleus. The neutron plays a role in binding the nucleus together, apparently adding attractive forces which predominate over the electrical repulsions among the protons. ... 

The interaction between two double layers was first considered by Voropaeva et a/.145 These concepts were used to measure the friction between two solids in solution. Friction is proportional to the downward thrust of the upper body upon the lower. However, if their contact is mediated by the electrical double layer associated with each interface, an electric repulsion term diminishes the downward thrust and therefore the net friction. The latter will thus depend on the charge in the diffuse layer. Since this effect is minimum at Eam0, friction will be maximum, and the potential at which this occurs marks the minimum charge on the electrode. 

Electrical repulsion between protons should cause a nucleus that contains more than one proton to fly apart. In Section 2H. we describe how the third type of fundamental force, called the strong nuclear force, acts within nuclei and generates enough attraction among nuclear particles to hold nuclei together. 

The most stable shape for any molecule maximizes electron-nuclear attractive interactions while minimizing nuclear-nuclear and electron-electron repulsions. The distribution of electron density in each chemical bond is the result of attractions between the electrons and the nuclei. The distribution of chemical bonds relative to one another, on the other hand, is dictated by electrical repulsion between electrons in different bonds. The spatial arrangement of bonds must minimize electron-electron repulsion. This is accomplished by keeping chemical bonds as far apart as possible. The principle of minimizing electron-electron repulsion is called valence shell electron pair repulsion, usually abbreviated VSEPR. 

Although nuclides with mass numbers around 60 are the most stable, the balance of electrical repulsion and strong nuclear attraction makes many combinations of protons and neutrons stable for indefinite times. Nevertheless, many other combinations decompose spontaneously. For example, all hydrogen nuclides with j4 > 2 are so... 

Neutrons readily induce nuclear reactions, but they always produce nuclides on the high neutron-proton side of the belt of stability. Protons must be added to the nucleus to produce an unstable nuclide with a low neutron-proton ratio. Because protons have positive charges, this means that the bombarding particle must have a positive charge. Nuclear reactions with positively charged particles require projectile particles that possess enough kinetic energy to overcome the electrical repulsion between two positive particles. 

The major impediment to fusion reactions is that the reacting nuclei must have very high kinetic energies to overcome the electrical repulsion between positive particles. The fusion of two hydrogen nuclei has the lowest possible repulsion barrier because it involves two Z — I nuclei. Even so, this reaction requires kinetic energies... 

The polycationic ammonium salt PEU can be chosen for increasing the ionic cloud in the electrical double layer, thus raising the electric repulsion between the gold particles in the sol. Small particles can be obtained (mean diameters between 3.1 and 4.2 nm) [24]. 

The distribution of metals between solution and the ferric hydroxide surface varies strongly with pH (Fig. 31.5). As discussed in Sections 10.4 and 14.3, pH exerts an important control over the sorption of metal ions for two reasons. First, the electrical charge on the sorbing surface tends to decrease as pH increases, lessening the electrical repulsion between surface and ions. More importantly, because hydrogen ions are involved in the sorption reactions, pH affects ion sorption by mass action. The sorption of bivalent cations such as Cu++,... 

For this reason, the work to overcome the electrical repulsion is diminished, the Cj. reduced, and the aggregation number increased. This model was checked experimentally with the adsorption at the water/air interface (, 22). 

At low temperatures (15 million K), reactions between helium nuclei are inhibited by electrical repulsion. On the other hand, the nuclear properties of lithium, beryllium and boron nuclei (Z = 3,4, 5), and in particular their stability, are such that they are extremely fragile, decaying at temperatures of only 1 million K. For this reason, they are not formed in appreciable quantities in stars and cannot serve to bridge the gap between helium and carbon, species noted for their nuclear stability but which, it should be recalled, occur only in minute amounts in nature. 

Just to reiterate what we have said, neutron capture is the only valid channel towards the extreme complexity of gold (Z = 79). Reactions involving charged particles are energetically unfavourable and moreover inhibited by insurmountable electrical barriers. Because of the strong electrical repulsion between heavy nuclei (which thus contain many protons), the classic thermonuclear fusion reactions are ineffective, and we are forced to accept the idea that nuclear species beyond iron are produced by a process other than thermonuclear fusion. This process is neutron capture. 

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