Alkanes

The Columbia Encyclopedia, an online encyclopedia, has an entry on hydrocarbon which does a good job of explaining alkanes. Hydrocarbons are organic compounds. They are composed of only two elements- carbon and hydrogen. There are sub-groups within hydrocarbons one of which is called alkanes. Quoting from the linked encyclopedic entry:

The alkanes are a homologous series of saturated aliphatic hydrocarbons. The first and simplest member of this series is methane, CH4; the series is sometimes called the methane series. Each successive member of a homologous series of hydrocarbons has one more carbon and two more hydrogen atoms in its molecule than the preceding member. The second alkane is ethane, C2H6, and the third is propane, C3H8. Alkanes have the general formula CnH2n+2 (where n is an integer greater than or equal to 1). Generally, hydrocarbons of low molecular weight, e.g., methane, ethane, and propane, are gases; those of intermediate molecular weight, e.g., hexane, heptane, and octane, are liquids; and those of high molecular weight, e.g., eicosane (C20H42) and polyethylene, are solids. Paraffin is a mixture of high-molecular-weight alkanes; the alkanes are sometimes called the paraffin series.

Alkanes consist of methane, ethane and propane which are generally encountered in a gaseous state, a heavier liquid group which include hexane, heptane and octane and solids like eicosane and polyethylene.


Reference:

The Columbia Encyclopedia; The online version; Columbia University Press