10 Structure and the homologous series
- Alkanes are open-chain hydrocarbons in which the carbon atoms are joined by single (sigma, σ) bonds only.
- The σ bond is strong and hard to break, so alkanes are chemically rather unreactive (they were once called "paraffins", meaning "little affinity").
First ten members:
11
Name
- methane
Formula
- CH₄
22
Name
- ethane
Formula
- C₂H₆
33
Name
- propane
Formula
- C₃H₈
44
Name
- butane
Formula
- C₄H₁₀
55
Name
- pentane
Formula
- C₅H₁₂
66
Name
- hexane
Formula
- C₆H₁₄
77
Name
- heptane
Formula
- C₇H₁₆
88
Name
- octane
Formula
- C₈H₁₈
99
Name
- nonane
Formula
- C₉H₂₀
1010
Name
- decane
Formula
- C₁₀H₂₂
Observations: general formula CₙH₂ₙ₊₂; each member differs from the previous by –CH₂– (methylene group); all names end in -ane, the prefix shows the number of carbons (meth-1, eth-2, prop-3, but-4, pent-5, hex-6, hept-7, oct-8, non-9, dec-10).
Homologous series: a group of organic compounds with the same general formula, the same functional group and similar chemical properties, whose successive members differ by a CH₂ group and whose physical properties change gradually.