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THE THEORY OF KOSSEL

Other atoms which do not have the stable structure of the noble gas, tend to change their number of electrons in such a way that the ion can take up the electronic structure of a noble gas, and it is therefore not merely fortuitous that all simple negative ions have this particular structure. The electrons which are taken up by the negative ions have been withdrawn from other atoms, and positive ions thus are formed simultaneously with negative ones. [Pg.30]

Many more positive than negative ions are formed in aqueous solutions. All alkali metals have a single positive charge, that is, they lose one electron per atom, and in the ionic state have the same number of electrons as are possessed by the preceding noble gas. [Pg.30]

But sulphur not only forms positive ions. As may be readily expected from its position in the periodic system where it occurs two places before and six places after a noble gas, it also forms divalent negative ions, as in K2S. It is the general rule that, in principle, all elements can form both positive and negative ions. However, only some of the combinations which can be written in this manner will actually occur as molecules because, as was seen in Section 4, a compound will only be formed if the potential energy decreases during the process, and this occurs only when ions of fairly low valency are formed. There are no compounds known that contain positive ions with a valency of nine the valency of negative ions is certainly never greater than four, and it is therefore quite easy to see why there is a limit to the number of compounds theoretically possible. [Pg.31]

Let us suppose that a molecule of Nad is formed from free atoms of Na and Cl. We can imagine a process in which an electron is first removed from a Na+ atom and is then transferred to the Cl atom, and the two ions so formed allowed to approach each other to within a distance given by the sum of their radii. The potential energy of the system will change in such a process and can be readily calculated. Such a process is, in a sense, fictitious, in so far as it cannot be carried [Pg.31]

Cobalt, as a result of its place in the periodic system, should have a valency of nine. It is, however, mostly divalent and occasionally tervalent. Phosphorus can be tervalent as well as pentavalent sulphur is hexavalent in SOs and tetravalent in S02. At low temperatures the valency is such that the energy is a minimum, and which compounds will be formed can only be predicted when the energy can be calculated accurately. [Pg.33]


The picture remains as a foundation for the discussion of bonding in terms of orbitals. There is much evidence in support of it. The idea of ionisation had been proposed in the 1880s and the difference between electrolytes, such as sodium chloride, and non-electrolytes, suchascarbon tetrachloride, had been observed quite some time before the theories of Kossel and Lewis. [Pg.25]


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