Alkanes are saturated compounds which have single bonds between carbon atoms and contain the maximum number of hydrogen atoms possible. Each carbon is flanked by four covalent bonds and each hydrogen atom shares one pair of electrons with a carbon atom, as illustrated in Figure 11.

The general formula for alkanes is CnHZn+2' The alkanes are colorless, practically odorless, insoluble in water, and readily soluble in nonpolar solvents such as benzene or ether.

Alkanes are low in reactivity. The reactions they do undergo are called halogenation, thermal decomposition (cracking), and combustion. These are summarized below.

Halogenation occurs when a hydrogen atom is replaced with a halogen atom. This is referred to as a substitution reaction. There is no limit to how many hydrogen atoms can be replaced in one molecule.

Figure 11 Alkane

Thermal decomposition or cracking is the process of breaking large molecules into smaller ones. Using heat as a catalyst, propane can be broken into methane and ethylene:

Combustion occurs when an alkane is burned, the products being carbon dioxide gas, water, and heat. These reactions are highly exothermic and as such the hydrocarbons are frequently used for fuel.