Chapter 12. Properties and Reactions of Alkanes

Physical Properties of Alkanes

IUPAC
name		 Molecular
Formula		 Structural
Formula		 Boiling
Point (°C)		 Melting
Point (°C)		 Density
(g/ml, 20°C)
Methane CH4 CH4 -161.5 -182.5 (gaseous)
Ethane C2H6 CH3CH3 -88.6 -183.3 (gaseous)
Propane C3H8 CH3CH2CH3 -42.1 -189.7 (gaseous)
Butane C4H10 CH3(CH2)2CH3 -0.5 -138.4 (gaseous)
Pentane C5H12 CH3(CH2)3CH3 36.1 -129.7 0.626
Hexane C6H14 CH3(CH2)4CH3 68.7 -95.3 0.659
Heptane C7H16 CH3(CH2)5CH3 98.4 -90.6 0.684
Octane C8H18 CH3(CH2)6CH3 125.7 -56.8 0.703
Nonane C9H20 CH3(CH2)7CH3 150.8 -53.5 0.718
Decane C10H22 CH3(CH2)8CH3 174.1 -29.7 0.730

Chemical Properties of Alkanes

Alkanes are usually stable at room temperature toward reactants such as concentrated aqueous acids or bases, an even the most reactive metals. Fluorine, however, attacks virtually all organic compounds, including the alkanes, to give mixtures of products. Hot nitric acid, chlorine, and bromine can also react with alkanes. The chlorination of methane can give the following compounds depending on the relative quantities of reactants used:
CH3Cl
methyl chloride
CH2Cl2
methylene chloride
CHCl3
chloroform
CCl4
carbon tetrachloride
When heated at high temperatures in the absence of air, alkanes can "crack," meaning that they break up into smaller molecules. The cracking of methane gives finely powered carbon and hydrogen gas. 
    high temperatures
CH4 =================> C + 2H2
The controlled cracking of ethane gives ethene ("ethylene"), which is an important raw material in the organic chemicals industry, used to make polyethylene plastics, ethyl alcohol, and ethylene gycol (an antifreeze). 
       high temperatures
CH3CH3 =================> CH2=CH2 + H2
ethane                    ethene