Saturated Hydrocarbons
Jean Brainard, Ph.D.
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Printed: August 25, 2016
AUTHOR
Jean Brainard, Ph.D.
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C HAPTER
Chapter 1. Saturated Hydrocarbons
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Saturated Hydrocarbons
• Define saturated hydrocarbon.
• Explain how saturated hydrocarbons are named.
• Identify shapes of saturated hydrocarbon molecules.
You can tell that this sponge is saturated with water because when it is squeezed, the water pours out. When
something is saturated with water, it already holds as much water as possible. Compounds called hydrocarbons,
which contain only carbon and hydrogen, can also be saturated, but not with water.
What Are Saturated Hydrocarbons?
Saturated hydrocarbons are hydrocarbons that contain only single bonds between carbon atoms. They are the
simplest class of hydrocarbons. They are called saturated because each carbon atom is bonded to as many hydrogen
atoms as possible. In other words, the carbon atoms are saturated with hydrogen. You can see an example of a
saturated hydrocarbon in the Figure 1.1. In this compound, named ethane, each carbon atom is bonded to three
hydrogen atoms. In the structural formula, each dash (-) represents a single covalent bond, in which two atoms share
one pair of valence electrons.
Q: What is the chemical formula for ethane?
A: The chemical formula is C2 H6 .
What’s in a Name?
Saturated hydrocarbons are given the general name of alkanes. 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
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FIGURE 1.1
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 the Table 1.1. 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.
TABLE 1.1: Small Alkanes and Their Properties
Alkane
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Chemical Formula
CH4
C2 H6
C3 H8
C4 H10
C5 H12
C6 H14
C7 H16
C8 H18
Boiling Point(◦ C)
-162
-89
-42
0
36
69
98
126
Melting Point(◦ C)
-183
-172
-188
-138
-130
-95
-91
-57
State (at 20 ◦ C)
gas
gas
gas
gas
liquid
liquid
liquid
liquid
Q: The Table 1.1 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 (see Figure 1.2). You can read about each type below.
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Chapter 1. Saturated Hydrocarbons
FIGURE 1.2
A) In a straight-chain molecule, all the
carbon atoms are lined up in a row like
cars of a train. The carbon atoms form
the “backbone” of the molecule.
B) In
a branched-chain molecule, at least one
of the carbon atoms branches off from
the backbone. C) In a cyclic molecule,
the chain of carbon atoms is joined at
the two ends to form a ring. Each ring
usually contains just five or six carbon
atoms, but rings can join together to
form larger molecules. A cyclic molecule
generally has higher boiling and melting
points than straight-chain and branchedchain molecules.
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4. Compare and contrast straight-chain, branched-chain, and cyclic alkanes.
Resources
MEDIA
Click image to the left or use the URL below.
URL: https://www.ck12.org/flx/render/embeddedobject/186330
References
1. Jodi So. Ethane is a saturated hydrocarbon . CC BY-NC 3.0
2. Christopher Auyeung. Alkanes can be both straight and branched molecules . CC BY-NC 3.0
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