Metal-hydrogen bond distances,

The actual spacings of the metal atoms in the surface will clearly be of importance in making one face of a metal crystal catalytically effective, and another not, depending on how closely the actual atom spacings approximate to the bond distances in alkene and hydrogen molecules. In practice only a relatively sma l proportion of the total metal surface is found to be catalytically effective—the so-called active points . These adsorb alkene strongly, and then desorb immediately the resultant alkane, thus becoming free for further alkene adsorption. 

On looking into the literature to see whether this value of d(ff) = 0.28 A is meaningful, it was found [1] that this is the value suggested by Pauhng [8] to account for the radius of H in the partially ioitic bonds in hydrogen halides and in alkali metal hydrides The author then used this value of d(H+) = 0.28 A to estimate the radii of alkali metal ions from the observed bond distances d(MH) j in the metal hydrides, MH. It was a pleasant surprise to find that,... 

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