Lattice energy group 1 hydrides

El 1.9 Hydrides decompose to elements. The MH lattice energy decreases down the group as the radius of cation increases thus LiH has the highest lattice energy and requires the highest decomposition temperature. Carbonates decompose to oxides. The difference in lattice energy between metal carbonate and metal oxide decreases down the group, which results in increased stability. 

The CH5 group, having a carbon atom in five-fold coordination, is called a carbonium ion. Carbonium-ion formation is an easier process in larger hydrocarbons, where the reaction is between the proton and the secondary or tertiary carbon atom, but is significantly more activated in the case of methane. The carbonium ion is the intermediate toward carbenium ions (3.29), where the positively charged carbon atom has a threefold coordination. Once formed, carbenium ions can be converted to hydrocarbons and new carbonium ions, in hydride transfer reactions, as in (3.31). Because of the lower activation energies of such reactions, the route via carbenium ions usually dominates over mechanisms involving carbonium ions. Reactions of the carbonium-ion type are terminated by a step in which a proton is transferred to the zeolite lattice. 

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