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By W G Frankenberg

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The surface of an adsorbent is not smooth but shows a roughness of molecular or higher dimensions. Many catalysts used in practice are deliberately prepared to contain a great number of capillaries of submicroscopic dimensions. There are many places on the highly developed inner surface areas of such microporous adsorbents where the adsorbed molecules come into direct contact with many more atoms of the adsorbent than would be possible if the surface were an ideally smooth plane. Such places where an increased number of atoms of the adsorbent are in direct contact with the adsorbed molecules form “active places” or “active spots” for van der Waals’ adsorption (28-30).

London (23) derived the following approximation for C: where a1and a2 are the polarizabilities of the participating atoms, h is Planck’s constant, and v 1 and v 2 are characteristic frequencies of the optical dispersion curve of the atoms. 2 are, therefore, characteristic energies in the dispersion equation; they are often approximately equal to the ionization energies of the atoms. If, therefore, no data on the dispersion are available, the following expression may be used : where I1 and I , are the ionization energies of the atoms.

Sharing of Electrons. I n the last example of the previous section we compared the adsorption of atomic hydrogen to the formation of a n alkali hydride. We may now ask whether surface combinations exist that may be compared t o chemical compounds of hydrogen in which this element is the electropositive partner, as is the case in hydrogen chloride. It is known that HC1 cannot be described as a purely ionic compound. Nevertheless some decades ago many attempts were made t o describe i t as a n ionic compound, in which the negative chloride ion was 44 3.

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