Many organic compounds found in nature contain rings of carbon atoms.  These compounds are known as cycloalkanes. Cycloalkanes have one or more rings of carbon atoms. Cycloalkanes only contain carbon-hydrogen bonds and carbon-carbon single bonds.  The simplest examples of this class consist of a single, un-substituted carbon ring, and these form a homologous series similar to the unbranched alkanes.

Like alkanes, cycloalkane molecules are often drawn as skeletal structures in which each intersection between two lines is assumed to have a carbon atom with its corresponding number of hydrogens.   Cyclohexane, one of the most common cycloalkanes is shown below as an example. 

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Cyclic hydrocarbons have the prefix "cyclo-". The IUPAC names, molecular formulas, and skeleton structures of the first ten cycloalkanes are given in Table 1.1. Note that the general formula for a cycloalkane composed of n carbons is C_nH_2n, and not C_nH_2n+2 as for alkanes.  Although a cycloalkane has two fewer hydrogens than the equivalent alkane, each carbon is bonded to four other atoms so are still considered to be saturated with hydrogen.

Table 1.1: Examples of Simple Cycloalkanes
Cycloalkane	Molecular Formula	Skeleton Structure
Cyclopropane	C3H6
Cyclobutane	C4H8
Cyclopentane	C5H10
Cyclohexane	C6H12
Cycloheptane	C7H14
Cyclooctane	C8H16
Cyclononane	C9H18
Cyclodecane	C10H20