3.33 Saturated Hydrocarbons
FIGURE 3.58
What’s in a Name?
Saturated hydrocarbons are given the general name ofalkanes. The name of specific alkanes always ends in –ane.
The first part of the name indicates how many carbon atoms each molecule of the alkane has. The smallest alkane is
methane. It has just one carbon atom. The next largest is ethane with two carbon atoms. The chemical formulas and
properties of methane, ethane, and other small alkanes are listed in theTable3.7. The boiling and melting points of
alkanes are determined mainly by the number of carbon atoms they have. Alkanes with more carbon atoms generally
boil and melt at higher temperatures.
TABLE3.7:Small Alkanes and Their Properties
Alkane Chemical Formula Boiling Point(°C) Melting Point(°C) State (at 20 °C)
Methane CH 4 -162 -183 gas
Ethane C 2 H 6 -89 -172 gas
Propane C 3 H 8 -42 -188 gas
Butane C 4 H 10 0 -138 gas
Pentane C 5 H 12 36 -130 liquid
Hexane C 6 H 14 69 -95 liquid
Heptane C 7 H 16 98 -91 liquid
Octane C 8 H 18 126 -57 liquidQ:TheTable3.7 shows only alkanes that have relatively few carbon atoms. Some alkanes have many more carbon
atoms. What properties might larger alkanes have?
A:Alkanes with more carbon atoms have higher boiling and melting points, so some of them are solids at room
temperature.
Shapes of Alkanes
Structural formulas are often used to represent hydrocarbon compounds because the molecules can have different
shapes and a structural formula shows how the atoms are arranged. Hydrocarbons may form straight chains,
branched chains, or rings (seeFigure3.59). You can read about each type below.
Summary
- Saturated hydrocarbons are hydrocarbons that contain only single bonds between carbon atoms. As a result,
each carbon atom is bonded to as many hydrogen atoms as possible. - Saturated hydrocarbons are given the general name of alkanes. The name of specific alkanes always ends in
–ane and has a prefix to indicate how many carbon atoms it has. - Hydrocarbons may form straight chains, branched chains, or rings. Ring-shaped hydrocarbons are called
cyclic hydrocarbons.
Vocabulary
- alkane: Saturated hydrocarbon that contains only single bonds between carbon atoms.
- saturated hydrocarbon: Hydrocarbon that contains only single bonds between carbon atoms.