Hydrocarbons Alkanes, Alkenes, and Alkynes

There are three types of hydrocarbon - alkanes, alkenes and alkynes. At upper secondary level knowledge of only the first four alkanes and first three alkenes is usually required. These are discussed in more detail as we go through the chapter. The alkynes have a carbon-carbon triple bond in their molecules. No knowledge of alkynes is expected at this level. 

As shown in T Figure 18.1, hydrocarbons can be broadly classified into four different types alkanes, alkenes, alkynes, and aromatic hydrocarbons. Alkanes are saturated hydrocarbons, while alkenes, alkynes, and aromatic hydrocarbons are all unsaturated hydrocarbons. Alkanes, alkenes, and alkynes can be differentiated based on their molecular formulas. 

All hydrocarbons—alkanes, alkenes, and alkynes—have similar physical properties. They are all insoluble in water but soluble in nonpolar solvents (Section 3.9). They are less dense than water and, like other homologous series, have boiling points that increase with increasing molecular weight (Table 7.2). Alkynes are more linear than alkenes, and a triple bond is more polarizable than a double bond (Section 3.9). These two features cause an alkyne to have stronger van der Waals interactions and, therefore, a higher boiling point than an alkene with the same number of carbons. 

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