Straight-Chain Alkanes
Ck12 Science
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Printed: August 19, 2016
AUTHOR
Ck12 Science
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C HAPTER
Chapter 1. Straight-Chain Alkanes
1
Straight-Chain Alkanes
• Define hydrocarbon and list classes of hydrocarbons.
• Define alkane.
• List the first ten alkanes and draw their structures.
As our country looks at the prospect of oil shortages in the future, we are searching for alternative transportation
fuel sources. One very viable possibility is propane gas. Power and acceleration for propane-powered vehicles are
comparable to gasoline-powered vehicles and fuel efficiency is greater. Propane has a higher octane rating than
regular gasoline, leading to much longer engine life. When properly structured, propane engines can produce lower
amounts of air pollution. We are seeing a growing use of propane in buses, trucks, and police cars. Pictured above
is a prototype of a minibus that will run on propane fuel. Maybe your next car will burn propane.
Straight-Chain Alkanes
Hydrocarbons
A hydrocarbon is an organic compound that is made up of only carbon and hydrogen. A hydrocarbon is the simplest
kind of organic molecule and is the basis for all other more complex organic compounds. Hydrocarbons can be
divided into two broad categories. Aliphatic hydrocarbons are hydrocarbons that do not contain the benzene group
or a benzene ring. Aromatic hydrocarbons contain one or more benzene rings. In this concept, we will discuss the
aliphatic hydrocarbons.
1
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Alkanes
An alkane is a hydrocarbon in which there are only single covalent bonds. The simplest alkane is methane, with the
molecular formula CH4 . The carbon is the central atom and makes four single covalent bonds to hydrogen atoms.
FIGURE 1.1
Methane is the simplest hydrocarbon and
is shown with a structural formula, a
ball-and-stick model, and a space-filling
model.
The next simplest alkane is called ethane (C2 H6 ) and consists of two carbon atoms with a single covalent bond
between them. Each carbon is then able to bond to three hydrogen atoms. The alkane series progresses from there,
increasing the length of the carbon chain by one carbon at a time. Structural formulas for ethane, propane (C3 H8 ),
and butane (C4 H10 ) are shown below.
These alkanes are called straight-chain alkanes because the carbon atoms are connected in one continuous chain with
no branches. Naming and writing structural and molecular formulas for the straight-chain alkanes is straightforward.
The name of each alkane consists of a prefix that specifies the number of carbon atoms and the ending -ane. The
molecular formula follows the pattern of Cn H2n+2 where n is the number of carbons in the chain. Table 1.1 lists the
first ten members of the alkane series.
TABLE 1.1: First Ten Members of the Alkane Series
2
Name
Molecular Formula
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
CH4
C2 H6
C3 H8
C4 H10
C5 H12
C6 H14
C7 H16
C8 H18
C9 H20
C10 H22
Condensed Structural Boiling Point (◦ C)
Formula
CH4
-161.0
CH3 CH3
-88.5
CH3 CH2 CH3
-42.0
CH3 CH2 CH2 CH3
0.5
CH3 CH2 CH2 CH2 CH3
36.0
CH3 CH2 CH2 CH2 CH2 CH3 68.7
CH3 CH2 CH2 CH2 CH2 CH2 CH
98.5
3
CH3 CH2 CH2 CH2 CH2 CH2 CH
125.6
2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH
150.7
2 CH2 CH3
CH3 CH2 CH2 CH2 CH2 CH2 CH
174.1
2 CH2 CH2 CH3
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Chapter 1. Straight-Chain Alkanes
Note that the table shows a variation of a structural formula called a condensed structural formula. In this formula,
the covalent bonds are understood to exist between each carbon and the hydrogens associated with it, as well as
between carbon atoms. This table also shows that the boiling points of the alkanes steadily increase as the length of
the carbon chain increases. This is due to an increase in the strength of the intermolecular attractive forces and is a
general feature of other organic molecules as well.
MEDIA
Click image to the left or use the URL below.
URL: https://www.ck12.org/flx/render/embeddedobject/185800
Review
1. What is a hydrocarbon?
2. What is an alkane?
3. Name the alkane that has five carbons in its chain.
•
•
•
•
aliphatic hydrocarbons: Hydrocarbons that do not contain the benzene group or a benzene ring.
alkane: A hydrocarbon in which there are only single covalent bonds.
aromatic hydrocarbons: Contain one or more benzene rings.
hydrocarbon: An organic compound that is made up of only carbon and hydrogen.
References
1. Courtesy of Yoichi Robert Okamoto, Environmental Protection Agency. http://commons.wikimedia.org/wik
i/File:PROTOTYPE_OF_A_MINI-BUS_WHICH_WILL_HAVE_A_MAXIMUM_SPEED_OF_SEVEN_MPH_AND_WILL_RUN_ON_PROPANE_GAS-LATER_TO_BE..._-_NARA_-_549652.tif .
2. (A) CK-12 Foundation - Steven Lai; (B) and (C) Ben Mills (Wikimedia: Benjah-bmm27). B) http://common
s.wikimedia.org/wiki/File:Methane-CRC-MW-3D-balls.png; (C) http://commons.wikimedia.org/wiki/File:Me
thane-CRC-MW-3D-vdW.png .
3. CK-12 Foundation - Christopher Auyeung. .
3