A saturated compound is one whose carbon atoms are joined by single covalent bonds only, as in the alkanes.
A saturated compound is one in which the carbon atoms are joined by single covalent bonds only, so the molecule holds as many hydrogen atoms as it possibly can. Malay: tepu · Chinese: 饱和.
Because every carbon–carbon bond is a single bond, there is no double bond that can open up, so saturated compounds do not undergo addition reactions. The alkanes are the saturated hydrocarbons of this chapter: they are relatively unreactive and their typical reactions are combustion and substitution with halogens in ultraviolet light, not addition. The word “saturated” is a useful shorthand, as soon as you know a compound is saturated, you know its carbons are full and its chemistry is limited.
Example. Ethane (C₂H₆) is saturated: its two carbon atoms are joined by a single bond and each carbon also bonds to three hydrogen atoms, using all four bonds. It burns readily but does not decolourise bromine water, because there is no C=C for the bromine to add across.
Confusion to avoid. Do not mix up saturated with unsaturated. A saturated compound has single bonds only and leaves bromine water unchanged; an unsaturated compound has at least one C=C double bond and rapidly decolourises bromine water at room temperature. This bromine-water test is the standard way to tell the two apart.
It helps to remember why the single bond makes such a difference. In a saturated molecule every carbon already uses all four of its bonds, so there is nothing for an extra atom to attach to without first breaking a strong bond, and that is why addition simply cannot happen. The only way to make an alkane react with another element is to swap an atom out for a new one, which is substitution, and even that needs the push of ultraviolet light. This limited, predictable behaviour is precisely why saturated hydrocarbons are so widely used as clean-burning fuels rather than as chemical feedstocks.
Being saturated is exactly what makes the alkanes the calm, unreactive baseline of the chapter, so the term is best learned side by side with unsaturated, the pair that SPM Chemistry regularly asks you to distinguish.
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